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Home , Chondrite, H chondrite, Maskelynite, Merrillite, Ordinary chondrite, Shock metamorphism

Article Shock History Assessed by Non-Destructive Analyses on Ca-Phosphates and in the Cangas de Onís

Alvaro Rubio-Ordóñez 1,* , Olga García-Moreno 1 , Luis Miguel Rodríguez Terente 2, Javier García-Guinea 3 and Laura Tormo 3

1 Departamento de Geología, Universidad de Oviedo, C/Jesús Arias de Velasco s/n, 33005 Oviedo, Spain 2 Museo de Geología, Universidad de Oviedo, C/Jesús Arias de Velasco s/n, 33005 Oviedo, Spain 3 Departamento de Geología, Museo Nacional de Ciencias Naturales (MNCN-CSIC), C/José Gutiérrez Abascal 2, 28006 Madrid, Spain * Correspondence: [email protected]

 Received: 21 February 2019; Accepted: 3 July 2019; Published: 9 July 2019 

Abstract: The Cangas de Onís regolith breccia is an H5-H6 that fell to in 1866. It is constituted by 60% H6-H5 clasts within an H5 clastic matrix. All clasts are affected by intense fissuration, with an intricate pattern filled by and , shock metamorphism of into . The chondrite is composed of low-Ca , and plagioclase as the main phases, with two types of phosphates, -kamacite blebs and troilite. The specimen was studied by micro-Raman spectroscopy, Fourier-transform infrared spectrophotometry (FTIR), spectral cathodoluminescence and computer tomography. The ease with which the specimens can be prepared for analysis using these techniques, and the speed with which relevant information can be obtained, make them excellent tools for the study of non-replaceable materials. Moreover, the Raman and FTIR results offer enough resolution to reveal heterogeneities in the shocked metamorphism throughout the specimen. The obtained results showed that the extent of the metamorphic conditions within the studied sample is heterogeneous, which leads us to believe that the last accretionary event that took place in this regolithic breccia was not significant enough to allow for overall homogenization.

Keywords: chondrite; raman; FTIR; non-destructive; chlorapatite; ; maskelynite

1. Introduction Non-destructive evaluation methods usually include different spectroscopy techniques to analyze both the surface and the interior of the objects under study. In museums, there are valuable stones such as that have had to be sliced in order to make polished petrographic sections with which to perform characterization studies. The application of non-destructive techniques makes it possible to perform practical studies while preserving these non-replaceable materials. New experimental data obtained using Raman spectroscopy of phosphates has opened the door to important petrogenetic data from these minerals. The position of the main phosphate peaks in Raman emissions is related to pressure in tuite and other orthophosphates in static pressure experiments [1–6]. In the same way, there are numerous studies that relate the morphology of the absorption spectra obtained by Raman and micro-FTIR in feldspars and other minerals to their pressure conditions [7–12]. These studies with high pressure phases (not founded in Cangas de Onis) can be useful to determine the spectral changes in our phases (related with shock metamorphism effects). Moreover, recent work has reassessed the classification of based on shock metamorphism, by more precisely redefining the characteristics of meteorites with greater metamorphism (types S5 and S6) [13].

Minerals 2019, 9, 417; doi:10.3390/min9070417 www.mdpi.com/journal/minerals Minerals 2019, 9, 417 2 of 15

2. Cangas de Onís The University of Oviedo Museum holds three fragments of the Cangas de Onís regolith breccia. This meteorite fell in Cangas de Onís (Asturias, Spain) on December 6, 1866, and several fragments were recovered. Recently, nine new fragments that have not been referenced until now were recognized in a donation from a private collector. This meteorite has been studied and characterized by different authors [14–19]. The Cangas de Onís regolith breccia is an H5-H6 ordinary chondrite, with approximately 60% of its makeup consisting of H6 and H5 clasts within an H5 clastic matrix. Mineralogically, all of the fragments are similar, being constituted by low-Ca pyroxene, olivine and plagioclase with kamacite, taenite and troilite as the main phases. Phosphates are common, and two different phosphates have been identified, chlorapatite and merrillite. Clasts in the breccia are affected by intense fissuration caused by shock. These fractures are partially filled by kamacite and/or troilite. The parental body was affected by an impact at least 7 Ma ago, when it left its stable [15,16]. Previous studies [17–19] have concluded that the Cangas de Onís regolith breccia had suffered at least two processes of and destruction with associated shock metamorphism and partial of and metallic minerals. The present study, however, is the first to use non- destructive techniques to trace the shock-metamorphic history of a chondrite regolith breccia. Here, we have performed a complete analysis of the breccia’s phosphates (chlorapatite and merrillite) and feldspars (plagioclase and maskelynite) through an array of non-destructive techniques (X-Ray Computerized Tomography Scan, Back-scattered electron images (BSE), Cathodoluminescence (CL), RAMAN spectroscopy and Fourier Transform Infrared (FTIR) spectrophotometry). Although the effects of shock metamorphism are best studied in tectosilicates (mainly and feldspars), we have found that these effects can also be detected in Ca-phosphates. After the characterization and classification of phosphates and feldspars in the Cangas de Onís regolith breccia, we analyzed the Raman and FTIR spectra of these phosphates together with the phases, to determine relative pressure conditions in different clasts within the Cangas de Onís breccia related to shock metamorphism.

3. Materials and Methods Data for the electron microscopy studies were collected at the physical-chemical facilities of the Museo Nacional de Ciencias Naturales, in Madrid (Spain). The environmental electron microscopy studies were performed using an FEI Inspect environmental scanning electron microscope (ESEM). The samples were observed with the BSE, energy dispersive Spectroscopy (EDS) and large field (LF) detectors. The ESEM resolution at low vacuum was 4.0 nm at 30 kV (BS). The accelerating voltage was 200 V to 30 kV and the probe current up to 2 µA was continuously adjusted, with low vacuum 0.45–0.55 torr, and a working distance of 10 mm. Sample EDS and mapping areas were carried out with an energy dispersive X-ray spectrometer (Oxford Instruments INCA Energy 200 Energy Dispersive System). The Inspect ESEM has a new coupled MonoCL3 Gatan probe to record CL spectra and panchromatic and monochromatic plots. It has a PA-3 photomultiplier tube covering a spectral range of 185–850 nm, which is more sensitive in the blue parts of the spectrum. A retractable parabolic diamond mirror and a photomultiplier tube were used to collect and amplify luminescence. The sample was positioned 16.2 mm beneath the bottom of the CL mirror assembly. The excitation for CL measurements was provided at 25 kV by an electron beam. Minerals 2019, 9, 417 3 of 15

In the same laboratory we obtained the micro-Raman and photoluminescence spectra of the spot samples. We used a Thermo-Fischer DXR Raman Microscope. The system has an Olympus BX-RLA2 Microscope and a Charge Coupled Device (CCD) detector (1024 256 pixels), motorized XY stage, × auto-focus and Olympus UIS2 series microscope lenses, all controlled through OMNIC 1.0 software (version 1.0.0.0, Thermo-Fischer Scientific Inc., Waltharn, MA, USA). The light at 532 nm of a frequency doubled Nd:YVO4 diode-pumped solid-state (DPSS) solid laser (maximum power 30 mW) was used for excitation. The DRX Raman has a point-and-shoot Raman capability of one-micron spatial resolution. We used the 20 objective of the confocal microscope together with the laser source at 532 nm and 6 × mW in laser mode, with power at 100%. The average spectral resolution in the Raman shift ranging 1 1 from 100 to 3600 cm− was 4 cm− , i.e., grating 900 lines/mm and 2 µm spot sizes. The system was operated under OMNIC 1.0 software, setting working conditions such as pinhole aperture of 25 µm, a bleaching time of 30 s, and four exposures with an average time of 10 s each. Infrared reflectance spectra were also obtained at the Servicios Científico-Técnicos of the University of Oviedo (Spain), using an FTIR spectrophotometer coupled to a Varian 620-IR and Varian 670-IR microscope. Analyses were obtained from circular 100 µm diameter regions. Micro-computed tomography (CT) scans were run on the 10.5 g piece of Cangas meteorite held in the meteorite exhibition hall of the Museo Nacional de Ciencias Naturales (MNCN) of Madrid, in order to observe volume, bulk density, and variations in internal density. For the volume and bulk density measurements we used a Nikon X-Tek CT-Scan device, also located at the MNCN laboratories, with a peak X-ray voltage of 146 kV and current of 65 mA, collecting 1583 sections at 1000 micro-seconds, being each section the average of four frames. The system operates with a tungsten X-ray tube and added filtration (0.875 mm Cu) to reduce beam hardening. Three- dimensional viewings and analyses of the obtained X-ray sections were performed using the program VG Studio Max Version 2.2. The auto-threshold feature determined the gray-scale intensity for 3-D surface segmentation and subsequent analysis. Surface reconstruction is useful for determining the volume and for correlating surface features with interior areas of interest. Microprobe data were also obtained for phosphates and feldspars from the meteorite. Analytical procedure and chemical data see Supplementary Tables S1–S3.

4. Results The detailed BSE-SEM images on the studied sample are shown in Figure1. In this process we recognized and measured all phosphates present in the thin section, identifying every phosphate grain in each breccia clast. The results indicate that the size of the phosphate crystals is variable. In addition, it depends on the clasts where they can be found. The largest phosphate crystals are found in the matrix (202 µm 122 µm), while the phosphates in the clasts are smaller (clast 1, 144 µm 9 µm; clast 2, 93 µm × × 68 µm; clast 3, 91 µm 52 µm; clast 4, 63 µm 45 µm). Moreover, the size of the phosphate crystals × × × is independent of the phosphate type. In the same areas as the phosphates, we likewise recognized and located all of the feldspars present. These crystals have variable sizes and are characterized by allotriomorphic morphologies, with micro-inclusions of olivine and pyroxene, and crosscut by Fe-Ni and troilite veins. Minerals 2019, 9, 417 4 of 15 Minerals 2018, 8, x FOR PEER REVIEW 4 of 15

Figure 1. Scanning electron images of the sample (A) Image photomontage of the analyzed sampleFigure surface. 1. Scanning Position electron of analyzed images of fields the sample and main (A) Image clasts photomontage are schematized of the in the analyzed upper sample left inset. (B)surface. Shock-melted Position fracture of analyzed in field fields 17 and (Clast main 1), clasts affecting are schematized an olivine . in the upper (C left) Textural inset. (B features) Shock- of analyzedmelted fracture phosphates in field in Clast17 (Clast 3 (field 1), affecting A04). ( Dan) Chlorapatiteolivine chondrule. in Clast (C) Textural 2 (field 38). features (E) Merrillite of analyzed over kamacitephosphates partially in Clast aff ected3 (field by A04). shocked (D) Chlorapatite veins of troilite. in Clast Opx: 2 (field Orthopyroxene; 38). (E) Merrillite Msk: Maskelynite;over kamaciteOl: Olivine;partially Tr: affected Troilite; by Kc: shocked Kamacite; veins Mer: of troilite. Merrillite; Opx: Orthopyroxene; Cl-Ap: Clorapatite. Msk: Maskelynite; Ol: Olivine; Tr: Troilite; Kc: Kamacite; Mer: Merrillite; Cl-Ap: Clorapatite. 4.1. Computerized Tomography Scan Orthogonal cross-sections of the micro-CT images displayed high-density regions, demonstrating heterogeneities in distribution. High atomic number features, such as metallic grains, coincide

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4.1. Computerized Tomography Scan Orthogonal cross-sections of the micro-CT images displayed high-density regions, demonstratingMinerals 2019, 9, 417 heterogeneities in mineral distribution. High atomic number features, such as metallic5 of 15 grains, coincide with bright voxels on micro-CT images, whereas the silicate matrix appears as a darkerwith bright gray voxelsmedium. on micro-CTThe Cangas images, fragment whereas in Figure the silicate 2, for matrixinstance, appears does not as a exhibit darker graya preferential medium. distributionThe Cangas fragmentof metallic in grains, Figure 2which, for instance, is consistent does notwith exhibit the external a preferential observation distribution of the offragment’s metallic surfaces.grains, which is consistent with the external observation of the fragment’s surfaces.

Figure 2. ((AA,,BB)) CT CT scan scan display display of of a a section section in in which which the the whitest whitest grains grains are are Fe-Ni, Fe-Ni, pale pale grey grey is is troilite, troilite, intermediateintermediate grey grey is iron-silicates, and darker areasareas are plagioclase.plagioclase. The The CT CT scan scan technique offers offers similar images in quality to those obtained by back backscattering,scattering, with with the the added benefit benefit of being able to observe an internal section using a non-destructive technique. (C–E) show section visualizations with observe an internal section using a non-destructive technique. (C–E) show section visualizations with different grades of density filter; in all probability the last image (E) corresponds to a plot of the spatial different grades of density filter; in all probability the last image (E) corresponds to a plot of the spatial distribution of Fe-Ni masses. distribution of Fe-Ni masses. 4.2. Cathodoluminescence Spectral Study 4.2. Cathodoluminescence Spectral Study The cathodoluminescence (CL) study of both types of phosphates, chlorapatite and merrillite, revealsThe two cathodoluminescence totally different spectra (CL) (Figurestudy 3of). both In the type cases of chlorapatitephosphates, (Figurechlorapatite3A), the and CL merrillite, spectra revealsare constituted two totally by adifferent relatively spectra wide peak(Figure at 5823). In nm th relatede case of to chlorapatite the presence (Figure of Mn2 +3A),as athe luminescence CL spectra 2+ areemission constituted activator. by a Lessrelatively significant wide peak peaks at show 582 nm up related at around to the 382 presence and 474 nm,of Mn and as are a luminescence related to the emissionpresence ofactivator. minor quantitiesLess significant of REE peaks and intrinsicshow up luminescence. at around 382 Inand the 474 case nm, of and merrillite are related (Figure to3 theB), presencethe obtained of minor spectra quantities are more of complicated, REE and intrinsic with several luminescence. peaks at diInff theerent case positions. of merrillite There (Figure are at least3B), thethree obtained main peaks, spectra at are 344, more 365 complicated, and 572 nm, with the last several one peaks being at related different to the positions. presence There of Mn are2 +atas least an 2+ threeactivator, main and peaks, the othersat 344, probably 365 and related572 nm, to the REE last or one tointrinsic being related luminescence. to the presence The rest of of Mn the peaksas an activator,may be related and the to variableothers probably quantities related of REE to elements. REE or to However, intrinsicthe luminescence. width and the The relative rest of intensity the peaks of maythe peaks be related are totally to variable different quantities from those of REE of elem chlorapatite.ents. However, There arethe nowidth substantial and the direlativefferences intensity in the ofindividual the peaks CL are spectra totally fordifferent each phosphate from those type. of chlorapatite. There are no substantial differences in the individual CL spectra for each phosphate type. Feldspars exhibited no differences throughout the spectra collected via CL. The presence of two peaks of similar intensity at 436 and 466 nm is characteristic of all feldspar spectra, and therefore will not be examined in this paper.

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Figure 3. Cathodoluminescence spectra of the two distinct phosphates. (A) Chlorapatite, high and low Figure 3. Cathodoluminescence spectra of the two distinct phosphates. (A) Chlorapatite, high and chlorine-content types, and (B) merrillite, high and low content. low chlorine-content types, and (B) merrillite, high and low calcium content. Feldspars exhibited no differences throughout the spectra collected via CL. The presence of two 4.3. Raman peaks of similar intensity at 436 and 466 nm is characteristic of all feldspar spectra, and therefore will not be examined in this paper. 4.3.1. Phosphates 4.3. RamanA systematic study of the Raman spectra of the phosphates was conducted on the Cangas sample. The results show that there are two different main spectra, one characteristic of chlorapatite 4.3.1. Phosphates and the other corresponding to merrillite (Figure 4). The spectra are characterized by the presence of largeA Raman systematic peaks study around of the 956 Raman and 972 spectra cm−1 in of merrillites the phosphates and only was ca. conducted 958 cm−1 onin chlorapatites. the Cangas sample. These Thebands results are showproduced that thereby the are υ1 two symmetric different stretching main spectra, mode one of characteristic (PO4)3−. These of chlorapatitemajor bands and are theaccompanied other corresponding by minor tobands merrillite between (Figure 10004 ).and The 1080 spectra cm−1 are, which characterized are related by to the asymmetric presence of υ3 1 1 largevibrations. Raman Minor peaks peaks around can 956 be observed and 972 cm at −aroundin merrillites 550 to 620 and cm only−1, and ca. are 958 also cm characteristic− in chlorapatites. of both 3 Thesephosphates bands [12,19,20]. are produced Characteristic by the υ1 bands symmetric related stretching to the presence mode of OH (PO−4 (near) −. These3600 cm major−1; graphical bands 1 arespectra accompanied end at 3650 by minorcm−1) were bands not between observed 1000 in and chlorapatite 1080 cm− or, which in merrillite. are related Moreover, to asymmetric peaks withυ3 1 vibrations.variable intensity Minor peaks appear can in be the observed merrillite at around spectra 550 between to 620 cm2050− , and and are2750 also cm characteristic−1. These bands of bothwere 1 phosphatesinterpreted [ 12as, 19photoluminescence,20]. Characteristic of bands REE, relatedreplacing to thestructural presence Ca of2+ OHin the− (near crystallographic 3600 cm− ; graphical structure 1 spectraof merrillite end at [20,21]. 3650 cm In− the) were case notof chloroapatite, observed in chlorapatiteno defined peaks or in can merrillite. be observed Moreover, in this peaks region, with but 1 variablea generalized intensity intensity appear inanomaly the merrillite is usually spectra present between in the 2050 same and area, 2750 cminterpreted− . These by bands the weresame interpretedmechanism as as photoluminescence in the case of merrillite. of REE, replacing structural Ca2+ in the crystallographic structure of merrillite [20,21]. In the case of chloroapatite, no defined peaks can be observed in this region, but a generalized intensity anomaly is usually present in the same area, interpreted by the same mechanism as in the case of merrillite.

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Figure 4. Raman spectra of two phosphate types: (a) Chlorapatite and (b) merrillite. Figure 4. Raman spectra of two phosphate types: (A) Chlorapatite and (B) merrillite. Figure 4. Raman spectra of two phosphate types: (a) Chlorapatite and (b) merrillite. 4.3.2. Feldspars 4.3.2. Feldspars 4.3.2.The Feldspars Raman spectra of the feldspars were also analyzed (Figure 5). The obtained spectra show no The Raman spectra of the feldspars were also analyzed (Figure5). The obtained spectra show no differences among the crystals. These spectra are characterized by the presence of two large Raman differencesThe Raman among spectra the crystals. of the feldspars These spectra were also are characterizedanalyzed (Figure by the5). The presence obtained of two spectra large show Raman no −1 −1 peaks around 478 and 510 cm1 (T–O and O–T–O bands), and minor bands at 171 cm1 (O–T and M– peaksdifferences around among 478 and the 510 crystals. cm− (T–O These and spectra O–T–O are bands), characterized and minor by bandsthe presence at 171 cm of− two(O–T large and Raman M–O), −1 −1 O), 290 to 3971 cm (O–T–O and−1 T–O–T bands) and 553 to 6861 cm . The intensity of−1 all the peaks, 290peaks to 397around cm− 478(O–T–O and 510 and cm T–O–T (T–O bands) and O–T–O and 553 bands), to 686 cm and− .minor The intensity bands at of 171 all thecm peaks, (O–T togetherand M– together with the− 1spectral positions, is similar to those obtained− 1from shocked plagioclase (e.g., withO), 290 the to spectral 397 cm positions, (O–T–O is and similar T–O–T to those bands) obtained and 553 from to shocked686 cm . plagioclase The intensity (e.g., ofreference all the peaks, [22]). reference [22]). The obtained spectra do not show a substantial presence of OH− in the analyzed Thetogether obtained with spectra the spectral do not showpositions, a substantial is similar presence to those of OHobtained− in the from analyzed shocked feldspar plagioclase grains, since(e.g., −1 feldspar grains, since the Raman spectrum ends in a low1 slope at 3650 cm . Under− a laser source at thereference Raman [22]). spectrum The obtained ends in aspectra low slope do atnot 3650 show cm a− substantial. Under a laser presence source of at OH 532 in nm, the the analyzed sample −1 532 nm, the sample exhibits two additional bands framed in the1 2000–3000 −cm1 region, which can be exhibitsfeldspar twograins, additional since the bands Raman framed spectrum in the ends 2000–3000 in a low cmslope− region,at 3650 whichcm . Under can be a attributablelaser source toat attributable to photoluminescence emission features from the accessorial maskelynite−1 . photoluminescence532 nm, the sample exhibits emission two features additional from thebands accessorial framed in maskelynite the 2000–3000 glass. cm region, which can be attributable to photoluminescence emission features from the accessorial maskelynite glass.

Figure 5. Raman spectra of plagioclase. Figure 5. Raman spectra of plagioclase. 4.4. Fourier Transform Infrared SpectroscopyFigure 5. Raman spectra of plagioclase. 4.4. Fourier Transform Infrared Spectroscopy 4.4.1. Phosphates 4.4. Fourier Transform Infrared Spectroscopy 4.4.1.A Phosphates complementary FTIR study was made on the same phosphate grains analyzed by Raman. As in the4.4.1. caseA Phosphates complementary of the Raman spectra, FTIR study two was different made spectra on the weresame observed,phosphate one grains characteristic analyzed by of Raman. Cl-apatite, As andin the theA case complementary other of the characteristic Raman FTIR spectra, ofstudy merrillite two was different made (Figure onspec6 the).tra Due same were to phosphate theobserved, nature onegrains of the characteristic analyzed equipment, by of allRaman. Cl-apatite, spectra As showinand the the case bands other of relatedthe characteristic Raman to thespectra, presenceof merrillite two different of water(Figure spec and 6)tra. CODue were2 presentto observed, the nature in the one of characteristicthe equipment, (located of Cl-apatite,all spectra in the 1 regionandshow the bands of other 1400–1800, related characteristic to 2300–2400the presence of merrillite and of 3500–4000water (Figure and CO cm6). 2−Due present). Into thethe in the casenature atmosphere of of Cl-apatite, the equipment, (located the FTIR in allthe spectraspectra region 1 are characterized by one major absorption band−1 at ca. 995 cm− and minor bands at 950, 1060 and showof 1400–1800, bands related 2300–2400 to the presenceand 3500–4000 of water cm and). CO In2 presentthe case in theof Cl-apatite,atmosphere the (located FTIR inspectra the region are 1 1080 cm . These bands are related to υ1 and υ3 stretching−1 mode [23], and are more complex in the ofcharacterized 1400–1800,− by2300–2400 one major and absorption 3500–4000 band cm at−1 ).ca. In 995 the cm case and of minorCl-apatite, bands theat 950,FTIR 1060 spectra and 1080 are case−1 of merrillite. Moreover, based on the intensity of the main peaks, two different spectra can be characterizedcm . These bands by one are major related absorption to υ1 and bandυ3 stretching at ca. 995 mode cm− 1[23], and and minor are bands more complexat 950, 1060 in the and case 1080 of distinguished for this phase. The first one (type A) has two main peaks at 970 and 1005 cm 1 and a cmmerrillite.−1. These Moreover, bands are relatedbased toon υ 1the and intensity υ3 stretching of the mode main [23], peaks, and aretwo more different complex spectra in the− cancase beof 1 symmetricmerrillite.distinguished distributionMoreover, for this phase.based of intensities Theon thefirst with intensity one minor (type of peaksA) the has at maintwo 860, main 1040,peaks, peaks 1060, two 1080at different 970 and and 1120 1005spectra cm cm− .−can1 In and thisbe a type of spectra, the asymmetric υ3 bands of (PO )3 are more important than the symmetric υ−1 bands. distinguishedsymmetric distribution for this phase. of intensities The first with one mi (typenor4 A)peaks− has at two 860, main 1040, peaks 1060, at 1080 970 and and 1120 1005 cm cm−.1 Inand this a symmetric distribution of intensities with minor peaks at 860, 1040, 1060, 1080 and 1120 cm−1. In this

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type of spectra, the asymmetric υ3 bands of (PO4)3− are more important than the symmetric υ1 bands. In the second type (type B), the distribution of the peaks is widespread with a main peak at 860 and 1 1 920 cm−1, ,and and peaks peaks with with less less intensities intensities are are to bebe foundfound atat 970,970, 10051005 andand 11201120 cmcm−−1. In In this case the symmetric υ1 bands of (PO )3 are dominant over the υ3 asymmetric bands. A minor peak at 730 cm 1 symmetric υ1 bands of (PO44)3− are dominant over the υ3 asymmetric bands. A minor peak at 730 cm−−1 can also be observedobserved inin thisthis typetype ofof merrillitemerrillite FTIRFTIR spectra.spectra. This peak has been interpreted as the symmetric vibration of the bond P-O-P in the P O [24]. It is possible that these two different spectra symmetric vibration of the bond P-O-P in the P22O7 [24]. It is possible that these two different spectra were caused by two didifferentfferent structural merrillites. The structural didifferencesfferences cancan be caused by partial substitutions in the mineral structure [[23–26].23–26]. At le leastast two samples show transitional spectra between these two main types.types.

Figure 6. FTIR spectra of chlorapatite and two different different types of spectra of merrillite, with bands attributed to atmospheric H22O and CO 2..

4.4.2. Feldspars 4.4.2. Feldspars As in the case of the phosphates, we analyzed the FTIR spectra of the same feldspar grains that As in the case of the phosphates, we analyzed the FTIR spectra of the same feldspar grains that were previously analyzed for Raman (Figure7). There were some additional di fficulties for the feldspar were previously analyzed for Raman (Figure 7). There were some additional difficulties for the analyses, due to the presence of micro-inclusions of olivine or pyroxene, generating mixed spectra feldspar analyses, due to the presence of micro-inclusions of olivine or pyroxene, generating mixed of both minerals. However, the di erent position of the main peaks, together with the possibility of spectra of both minerals. However,ff the different position of the main peaks, together with the obtainingpossibility inclusion-free of obtaining crystalinclusion-free analyses crystal on some analyses feldspar, on ultimatelysome feldspar, yielded ultimately sound results. yielded sound results.The obtained maskelynite spectra show a typical profile with a wide peak between 930 and 1 υ 940 cmThe− obtainedcorresponding maskelynite to symmetric spectra show1 Si–(Al)–O a typica bands,l profile and with smaller a wide bands peak at between 640 that 930 correspond and 940 to δ O–Si(Al)–O, 720 and 750 cm 1 (Si–Al(Si) and Si–Si υ1 bands) and 1050 cm 1 (e.g., [12]). In those cm−1 corresponding to symmetric− υ1 Si–(Al)–O bands, and smaller bands at 640− that correspond to δ spectra with olivine micro-inclusions there is a narrower main peak at around 940 cm 1, and the minor O–Si(Al)–O, 720 and 750 cm−1 (Si–Al(Si) and Si–Si υ1 bands) and 1050 cm−1 (e.g., [12]).− In those spectra peaks are much less intense, but the δ O–Si(Al)–O band is present at 640 cm 1. with olivine micro-inclusions there is a narrower main peak at around 940 cm− −1, and the minor peaks are much less intense, but the δ O–Si(Al)–O band is present at 640 cm−1.

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FigureFigureFigure 7. 7.7. FTIR FTIRFTIR spectra spectraspectra of ofof maskelynite maskelynite/plagioclasemaskelynite/plagioclase/plagioclase in inin three threethree di ff differentdifferenterent types, types,types, based basedbased on peak onon peakpeak positions positionspositions and diandandfferent differentdifferent grades gradesgrades of crystallinity. ofof crystallinity.crystallinity. 5. Discussion 5.5. DiscussionDiscussion Various studies on the effects of pressure on the crystallization of phosphates [2–4,26,27] have VariousVarious studiesstudies onon thethe effectseffects ofof pressurepressure onon ththee crystallizationcrystallization ofof phosphatesphosphates [2–4,26,27][2–4,26,27] havehave determined that the main peaks in the Raman spectra are displaced to higher values as pressure determineddetermined thatthat thethe mainmain peakspeaks inin thethe RamanRaman specspectratra areare displaceddisplaced toto higherhigher valuesvalues asas pressurepressure increases. If we analyze the obtained Raman spectra focusing only on peak position, we can observe a increases.increases. IfIf wewe analyzeanalyze thethe obtainedobtained RamanRaman spectraspectra focusingfocusing onlyonly onon peakpeak position,position, wewe cancan observeobserve certain degree of variability (Figure8A,B). Peaks at lower positions are found in crystals of chlorapatite aa certaincertain degreedegree ofof variabilityvariability (Figure(Figure 8A,B).8A,B). PeaksPeaks atat lowerlower positionspositions areare foundfound inin crystalscrystals ofof and merrillite located in nearby locations in the sample. This observation may be related to different chlorapatitechlorapatite andand merrillitemerrillite locatedlocated inin nearbynearby locationslocations inin thethe sample.sample. ThisThis observationobservation maymay bebe relatedrelated shock metamorphic conditions, with relative minor pressure effects in some clasts when compared toto differentdifferent shockshock metamorphicmetamorphic conditions,conditions, withwith relarelativetive minorminor pressurepressure effectseffects inin somesome clastsclasts whenwhen with others. Moreover, there is a significant observable effect related to the main shock-melted veins comparedcompared withwith others.others. Moreover,Moreover, therethere isis aa significsignificantant observableobservable effecteffect relatedrelated toto thethe mainmain shock-shock- and fractures in the clasts (Figure9), as Raman spectra peaks in grains close to these fractures show meltedmelted veinsveins andand fracturesfractures inin thethe clastsclasts (Figure(Figure 9),9), asas RamanRaman spectraspectra peakspeaks inin grainsgrains closeclose toto thesethese higher displacement values. fracturesfractures showshow higherhigher displacementdisplacement values.values.

Figure 8. Bivariate diagrams of main peak positions in the Raman spectra, with their correlation Figure 8. Bivariate diagrams of main peak positions in the Raman spectra, with their correlation coeFigurefficients. 8. Bivariate (A) Raman diagrams Cl-apatite of main peaks. peak (B) Ramanpositions merrillite in the peaks.Raman spectra, with their correlation coefficients.coefficients. ((AA)) RamanRaman Cl-apatiteCl-apatite peaks.peaks. ((BB)) RamanRaman merrillitemerrillite peaks.peaks.

Minerals 2019, 9, 417 10 of 15 Minerals 2018, 8, x FOR PEER REVIEW 10 of 15 Minerals 2018, 8, x FOR PEER REVIEW 10 of 15

Figure 9. Interpretative scheme of the analyzed probe (same as Figure 1), including clast limits and Figure 9. Interpretative scheme scheme of of the the analyzed probe probe (s (sameame as Figure 11),), includingincluding clastclast limitslimits andand main shock-melted fractures (e.g., detailed image). An approximate pressure effect deduced from the main shock-melted fractures (e.g., detailed image) image).. An An approximate approximate pressure pressure effect effect deduced from the Raman and FTIR peak positions observed in the phosphates and maskelynite have been included Raman and FTIR peak positions observed in the phosphates and maskelynite have been included (green, relatively low pressure; orange, intermediate; red, relatively high pressure). (green, relatively lowlow pressure;pressure; orange,orange, intermediate;intermediate; red,red, relativelyrelatively highhigh pressure).pressure). The effect of shock metamorphism in the observed FTIR spectra is more difficult to interpret, as The effect effect of shock metamorphism in the observed FTIR spectra is more difficult difficult to interpret, as these spectra present a greater degree of uncertainty. Although there is no evidence to support the these spectra present a greater degree of uncertainty. Although there is no evidence to support the pressure effect (Figure 10), the peak positions nevertheless appear to be related to certain differences pressure eeffectffect (Figure(Figure 10 10),), the the peak peak positions positions nevertheless nevertheless appear appear to to be be related related to to certain certain di ffdifferenceserences in in the spectra. The peak position values in the type-B FTIR spectra samples are lower than in the type- inthe the spectra. spectra. The The peak peak position position values values in in the the type-B type-B FTIR FTIR spectra spectra samples samples are are lower lower than than in in the the type-A type- A spectra. Transitional samples, such as 27 or 18, are located between two populations (Figure 11B). Aspectra. spectra. Transitional Transitional samples, samples, such such as as 27 27 or or 18, 18, areare locatedlocated betweenbetween two populations (Figure 11B).11B). The positions with the highest P conditions according to the Raman peak position diagrams are The positionspositions withwith the the highest highest P conditionsP conditions according according to the to Raman the Raman peak positionpeak position diagrams diagrams are located are located in opposite locations in the FTIR peak position diagram (e.g., samples 20 and 13). locatedin opposite in opposite locations locations in the FTIR in the peak FTIR position peak position diagram diagram (e.g., samples (e.g., samples 20 and 13). 20 and 13).

FigureFigure 10.10. BivariateBivariate diagramsdiagrams ofof mainmain peakpeak positionposition inin thethe FTIRFTIR spectra,spectra, withwith theirtheir correlationcorrelation Figure 10. Bivariate diagrams of main peak position in the FTIR spectra, with their correlation coecoefficients.fficients. ( (AA)) FTIR FTIR Chlorapatite Chlorapatite peaks. peaks. (B) (FTIRB) FTIR merrillite merrillite peaks peaks for type-A for type-A FTIR FTIRspectra spectra (blank coefficients. (A) FTIR Chlorapatite peaks. (B) FTIR merrillite peaks for type-A FTIR spectra (blank (blanksquares) squares) and type-B and type-B FTIR spectra FTIR spectra (crossed-out (crossed-out squares), squares), with their with correlation their correlation coefficients. coefficients. squares) and type-B FTIR spectra (crossed-out squares), with their correlation coefficients. The pressure dependence of band position in the Raman and FTIR spectra of feldspars has The pressure dependence of band position in the Raman and FTIR spectra of feldspars has previously been studied by several authors (e.g., references [28,29]). For example, [28] indicate that previously been studied by several authors (e.g., references [28,29]). For example, [28] indicate that the crystallinity of Sr-feldspar decreases as pressure increases, with broader peaks at higher pressure the crystallinity of Sr-feldspar decreases as pressure increases, with broader peaks at higher pressure than at lower pressure for micro FTIR. For pressures up to 10 GPa, peak positions are modified and than at lower pressure for micro FTIR. For pressures up to 10 GPa, peak positions are modified and

Minerals 2018, 8, x FOR PEER REVIEW 11 of 15 move to higher positions, but for pressures above 10 GPa this relationship is reversed. As established in previous studies [17,19], these pressure conditions throughout the Cangas de Onís regolith breccia’s history of accretion, disintegration and reaccretion were easily determined. In all likelihood, it was repeated impacts on the surface of the body that formed the regolith [30]. The Cangas de Onís regolith breccia has been classified as type S3 [13,30], according to the presence of melt pockets and opaque shocked veins, but we associate the secondary Raman-PL emission features framed in the 2000–3000 cm−1 region with accessorial maskelynite glass infilling feldspar fissures, since [31] has analyzed hydrogenated vitreous silica by Raman, attributing the spectrum band at ~2255 cm−1 to the vibration of SiH groups. Through experimentation, we have observed that these bands display full size in recently formed or heated feldspar glass or crystals. The photoluminescence band intensities of the 2000–3000 cm−1 spectral region decrease gradually through time following glass relaxation mechanisms; indeed, the Cangas fragments were heated more than a century ago, which explains this low emission. The broad FTIR bands observed for feldspars in the Cangas de Onís regolith breccia reflect, in the same way as phosphates (Figure 11A,B), variations that can be correlated to clast type and proximity to shock-melted veins (Figure 9). This correlation, together with the phosphate results, allows us to interpret that the chondritic matrix has relatively higher pressure effects in these two species than in some of the clasts. Moreover, the clasts show variation in these pressure effects that are spatially related to some of the shock-melted veins. In Clast 1, higher values are associated with two areas related to a shock-melted vein (Figure 9): one in a lower part where a complex fracture pattern developed; and a second area at the end of said shock-melted vein. Lower pressure values Minerals 2019, 9, 417 11 of 15 are associated with areas where these shock-melted veins are not well developed. The same scheme can be observed in Clast 2.

Figure 11. BivariateBivariate diagrams diagrams of of main main peak peak position position in in the the FTIR spectra, with their correlation coefficients.coefficients. ( (AA)) Bivariate Bivariate diagram diagram of of peak peak position position and and the the gap gap between between peak peak bands bands 1080–660 1080–660 nm. nm. (B) BivariateBivariate diagram diagram of of the the same same peak peak position positi ason in Aas and in peakA and bands peak 1080–950 bands nm;1080–950 green, maskelynitenm; green, maskelyniteFTIR spectra FTIR type A;spectra yellow, type maskelynite A; yellow, FTIR maskelynite spectra type FTIR B; spectra red, maskelynite type B; red, FTIR maskelynite spectra type FTIR C. spectra type C. The pressure dependence of band position in the Raman and FTIR spectra of feldspars has previouslyThis evidence been studied allows by us several to be authorsmore precise (e.g., referencesin addressing [28, 29the]). complex For example, accretional [28] indicate history that of the the Cangascrystallinity de Onís of Sr-feldspar regolith breccia. decreases A previous as pressure intricate increases, scenario with was broader depicted peaks by at [17], higher with pressure at least thantwo accretionat lower pressureevents evidenced for micro by FTIR. the Forformation pressures of a up bre toccia 10 GPa,within peak the positions breccia. In are that modified paper a and detailed move mineralogicalto higher positions, and textural but for study pressures evidenced above the 10 occurr GPa thisence relationship of several impact is reversed. events As in establishedthe formation in ofprevious the studies [17 parent,19], these body. pressure One of conditionsthe last impa throughoutct events reported the Cangas by these de On authorsís regolith is related breccia’s to thehistory formation of accretion, of the disintegrationregolith breccia and on reaccretionthe surface wereof the easily parent determined. body. Lithification In all likelihood, was caused it was by impact,repeated or impacts additional on collisions the surface in space, of the after body the that blocks formed of the the breccia regolith had [become30]. The detached Cangas from de On theís parentregolith body. breccia has been classified as type S3 [13,30], according to the presence of melt pockets and opaque shocked veins, but we associate the secondary Raman-PL emission features framed in the 2000–3000 cm 1 region with accessorial maskelynite glass infilling feldspar fissures, since [31] has − 1 analyzed hydrogenated vitreous silica by Raman, attributing the spectrum band at ~2255 cm− to the vibration of SiH groups. Through experimentation, we have observed that these bands display full size in recently formed 1 or heated feldspar glass or crystals. The photoluminescence band intensities of the 2000–3000 cm− spectral region decrease gradually through time following glass relaxation mechanisms; indeed, the Cangas fragments were heated more than a century ago, which explains this low emission. The broad FTIR bands observed for feldspars in the Cangas de Onís regolith breccia reflect, in the same way as phosphates (Figure 11A,B), variations that can be correlated to clast type and proximity to shock-melted veins (Figure9). This correlation, together with the phosphate results, allows us to interpret that the chondritic matrix has relatively higher pressure effects in these two species than in some of the clasts. Moreover, the clasts show variation in these pressure effects that are spatially related to some of the shock-melted veins. In Clast 1, higher values are associated with two areas related to a shock-melted vein (Figure9): one in a lower part where a complex fracture pattern developed; and a second area at the end of said shock-melted vein. Lower pressure values are associated with areas where these shock-melted veins are not well developed. The same scheme can be observed in Clast 2. This evidence allows us to be more precise in addressing the complex accretional history of the Cangas de Onís regolith breccia. A previous intricate scenario was depicted by [17], with at least two accretion events evidenced by the formation of a breccia within the breccia. In that paper a detailed mineralogical and textural study evidenced the occurrence of several impact events in the formation of the H Chondrite . One of the last impact events reported by these authors is related to Minerals 2018, 8, x FOR PEER REVIEW 12 of 15

The data provided in the present paper complete the scenario described by these authors. After the thermal metamorphism into the parental body (around 100 km of diameter and below 750 K), the

Mineralsfirst process2019, 9 ,of 417 accretion observed took place under relatively low pressure conditions (<10 12GPa), of 15 with temperatures below 750 K. During this process, the different grains of taenite and kamacite were formed with a fissural diffusion into the first cracks developed. The different silicates underwent thefusion formation processes of theafter regolith cooling. breccia At some on thelater surface time, ofthe the body parent or bodies body. Lithificationexhibiting these was causedfragments by impact,underwent or additional impact rupture, collisions with in space,the formation after the blocksof shocked of the brecciaveins, cracks had become and microcracks detached from in the parentmaterials, body. and the phosphates registering an increase in ambient pressure (<10 GPa). Through these fissures,The sulfurous data provided vapors in penetrat the presented, producing paper complete the partial the transfor scenariomation described of the by taenite-kamacite these authors. Afterinto the thermal and metamorphism troilite (Figure into 12A,B). the parental body (around 100 km of diameter and below 750 K), the firstLastly, process the offinal accretion accretion observed process, took after place the under formation relatively of low the pressure , conditions involved (<10 GPa), the withdeformation temperatures of the below clasts 750 under K. During fragile this conditions, process, thewith diff theerent development grains of taenite of planar and kamacite fissures wereand formedpseudotaquilites with a fissural (Figures diffusion 1B and into 12C). the firstThis cracks process developed. involved Thea major different local silicatesincrease underwent of both pressure fusion processes(>10 GPa) afterand temperature cooling. Atsome (>750later K), with time, the the development body or bodies of minor exhibiting melt thesepockets, fragments and locally underwent causes impactthe reequilibrium rupture, with of the formationolivine wi ofth shockedneoformation veins, of cracks chromite and microcracks (Figure 12C). in theThis materials, diffusion andcan thebe phosphatesrelated with registering an increase an in increase the oxidant in ambient conditions, pressure as occurs (<10 GPa).in other Through meteorites these [31], fissures, but in sulfurous this one vaporsrelated penetrated,with a last producingphase of acretion the partial (not transformation with a reflection of theof the taenite-kamacite earliest traces into of the pentlandite solar system and troiliteformation, (Figure as in 12 referenceA,B). [32]

Figure 12. Scanning Electron Microscope images (left) and composition maps (right). (A) Sulfurous veinsFigure surrounding 12. Scanning a taenite-kamacite Electron Microscope grain. images (B) Sulfurous (left) and veins composition filling olivine maps grains, (right). and transformation (A) Sulfurous ofveins taenite-kamacite surrounding grains a taenite-kamacite into troilite-pentlandite. grain. ( BC)) ChromiteSulfurous formation veins filling by Cr-di olivineffusion grains, from olivine and andtransformation Fe-alteration of of taenite-kamacite kamacite. Msk: Maskelynite;grains into troilite-pentlandite. Ol: Olivine; Tr: Troilite; (C) Kc:Chromite Kamacite; formation Pl: Plagioclase; by Cr- Cr:diffusion Chromite. from olivine and Fe-alteration of kamacite. Msk: Maskelynite; Ol: Olivine; Tr: Troilite; Kc: Kamacite; Pl: Plagioclase; Cr: Chromite. Lastly, the final accretion process, after the formation of the solar system, involved the deformation of the clasts under fragile conditions, with the development of planar fissures and pseudotaquilites (Figures1B and 12C). This process involved a major local increase of both pressure ( >10 GPa) and temperature (>750 K), with the development of minor melt pockets, and locally causes the reequilibrium Minerals 2019, 9, 417 13 of 15 of the olivine with neoformation of chromite (Figure 12C). This diffusion can be related with an increase in the oxidant conditions, as occurs in other meteorites [31], but in this one related with a last phase of acretion (not with a reflection of the earliest traces of the solar system formation, as in reference [32].

6. Conclusions By using non-destructive analytical techniques to study materials preserved in the collections of museums and other institutions, it is possible to obtain better results and a deeper knowledge of the studied objects than with more traditional destructive techniques. In the case of the Cangas de Onís meteorite, FTIR and Raman spectroscopy studies have enabled us to determine the presence of different mineral species and relate these phases to differences in the shock-metamorphic conditions that the material underwent. Such studies make it possible to determine and interpret the evolutionary history of meteorites with greater precision. In the study of the Cangas de Onís meteorite, we can see that the extent of the metamorphic conditions within one studied sample is heterogeneous, which leads us to believe that the last accretionary event that took place in this regolithic breccia was not significant enough to allow for overall homogenization. All of this serves to demonstrate that these methods can enable us to classify meteorites according to the classic scheme while using techniques that are not only quick and affordable, but most importantly are non-destructive as well. In addition, the spectral variations observed in this study can be useful to interpret and model remotely sensed spectra of planetary and asteroidal surfaces (e.g., reference [33]).

Supplementary Materials: The following are available online at http://www.mdpi.com/2075-163X/9/7/417/s1, Table S1: Apatite EPMA; Table S2: Merrillite EPMA; Table S3: Plagioclase EPMA. Author Contributions: Conceptualization, A.R.-O. and O.G.-M.; Methodology, A.R.-O., O.G.-M. and J.G.-G.; Resources, L.M.R.T., J.G.-G. and L.T. Writing-Original Draft Preparation, A.R.-O. and O.G.-M.; Writing-Review & Editing, A.R.-O. and O.G.-M.; Supervision, A.R.-O. and O.G.-M. Funding: Financial support was provided by Researches Projects UNOV-13-EMERGENTE-17 and UNOV-12-MB-04 from the University of Oviedo. Conflicts of Interest: The authors declare no conflict of interest.

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