B"H Hibonite Properties and Terrestrial Occurrence Griffin, W. L. (1), Toledo, V. (2), Gain, S.E.M. (1), Huang, J-X. (1) 1. ARC Centre of Excellence for Core to Crust Fluid Systems and GEMOC, Macquarie University, NSW 2109, Australia 2. Shefa Yamim (A.T.M.) Ltd., Akko, Israel Composition: CaAl12O19: Al2O3 ca 85%, CaO 8% by weight. Substitution of Ce, La, Mg, Fe, Ti, Si, giving (Ca,Ce)(Al,Ti,Mg,Fe)12O19. Crystal Structure Hexagonal - Dihexagonal Dipyramidal Space Group: P 63/mmc Properties Cleavage: {0001} good Color: Yellow to red-brown to black. Density: 3.84 Diaphaneity: Transparent to Opaque Fracture: Subconchoidal Habit: Prisms, platy on {0001}, steep pyramids to several cm Hardness: 7.5-8 Luster: Vitreous Refractive index: 1.790-1.807 Streak: brown Dichroism (e): - Dichroism (w): - Optical Data: Uniaxial (-),ε = 1.79(1) . ω = 1.807(2) The historical background of confined to microscopic grains; it is one of the Hibonite, and its use as a gemstone oldest minerals in the solar system, and may The mineral is named after Paul Hibon, who occur in interstellar dust. found cm-sized black crystals in a placer deposit in Madagascar in 1953, and sent them Its use as a gemstone has been limited, and to Jean Behier for examination. After further largely confined to placer material from analysis by C. Gillemin at the Sorbonne, It was Myanmar, which yields transparent yellow described as a new mineral in 1956 (Curien et crystals up to 1-2 cm across. al., Am. Min, V. 42, p. 119). Later on hibonite was assigned as a common Type Locality constituent of refractory Calcium-Aluminum The type locality is the Esiva eluvials, Esiva, Inclusions in meteorites, mainly carbonaceous Maromby Commune, Tulear Province, chondrites. Meteoritic hibonite is blue, and Madagascar. The type material was probably derived from nearby skarn deposits. October, 2016 Page 1 from 9 Occurrence metamorphism in the area. The origin of the heat which metamorphosed these 1. Hibonite occurs frequently in thorianite- rocks is thought to be due to bearing skarns, which are widespread in spontaneous isochemical combustion of Pan-African (565-515 Ma) granulites in bituminous compounds. The intensity of belts extending through Madagascar metamorphism correlates to access to (including the type locality) and oxygen; hydrocarbons are widespread in Tanzania. At least 20 localities are surrounding rocks but are absent in the known in Madagascar, with hibonite metamorphosed beds. One paper argues crystals up to 10 cm long. It also occurs that combustion was due to in xenoliths of Ca-Al granulites brought hydrocarbon fluids and heat released up in basanites in the Chyulu Hills from a “fossil mud volcano”. The Volcanic Field in Kenya, also part of the rationale for this interpretation is not Pan-African belt. In the thorianite- clear. “Hatrurim Formation" is often bearing skarns, which form metasomatic used as a locality name, but it is really a lenses in C-Al rich rocks, probably geological unit, outcropping at many originally anorthosites. Usually early localities, spread over three countries. corundum + spinel + scapolite Gross (1977) did not describe hibonite asemblages are altered to anorthite from Hatrurium formation, but it now +calcite+ scapolite, and hibonite appears in most mineral lists from the crystallizes at the expense of corundum area. and spinel. P-T conditions are estimated 4. Hibonite has recently been reported as at 700-800 °C, 3.5 kbar. The two transparent orange-brown crystals crystallization of hibonite implies a very (0.23, 0.71 gm) said to be recovered low silica activity and probably high CO2. from the gem gravels of Myamar. 2. Hibonite has been reported as black- There is no other information, but brown tabular crystals up to 3 cm across other gems from these placers are in calcitic marbles from the Tashelga- derived from high-temperature Malzaskaya region in Siberia. These granulite-facies carbonate rocks, hibonites are notably high in Fe3+, and similar to those in Madagascar. V-rich minerals (goldmanite, tashelgite, However, like the SY hibonite (see mukhinite….) are found in the same below) the Myanmar material has very rocks. low contents of Fe, but Ti and Mg are 3. The Hatrurim formation (formerly both present at levers of 4-5 wt% known as the “Mottled Zone”) is a oxide. This distinguishes it from most unique rock complex exposed mainly in of the hibonite found in granulite- the Judean Desert. It was depsoited as a facies rocks. The Myanmar grains also thin marine, bituminous chalk-marl contain inclusions of corundum and formation of Campanian to Neogene fluorite, giving another link to the SY age. Some parts of the Ghareb occurrences. formation contain up to 26% organic 5. Hibonite is present in two forms in SY matter and can be classified as oil shales. samples: one type is found in primary Today the rocks in a number of areas, sources of Mt. Carmel and the other is especially the Jerusalem-Jericho area, alluvial, recovered from the Kishon are largely composed of high- catchment, the main drainage in temperature metamorphic minerals northern Israel (1022 sq km, 77 km corresponding to the sanidinite and long). This catchment has been divided pyroxene-hornfels facies (up to 1000 °C, in the SY Geological model iinto three very low P). However, there is no segments: Proximal, Mid, Distal indication of igneous activity or contact Reaches. October, 2016 Page 2 from 9 6. In the framework of mineralogical of native vanadium, and a typical analysis of target minerals from these association with grossite (CaAl4O7) and localities within SY's exploration permit fluorite. The second type of occurrence areas, SY sent what was then recognized is interstitial to corundum crystals in as corundum of Non-Gem Corundum corundum aggregates, associated with type (NGC). Later, the Macquarie GEMOC grossite. The SY hibonite does not team found that a portion of these contain significant amounts of Fe or Ti. corundums are actually hibonites (!). 9. Finally, hibonite is a common phase in Thus, this was the first discovery of the refractory Calcium-Aluminum hibonite in the SY exploration project. As Inclusions (CAIs) found in carbonaceous mentioned above, it should be noted chondrite meteorites. As such, it that hibonite has already been found in represents some of the oldest crystalline southern Israel – at least mentioned in material in the Solar system. minerals from lab analysis on specimens there (see section 3). SY samples reach up to few mm in size, as crystals (see Conditions of Formation: section 8 and photos below). Oxygen fugacity (fO2): Hibonite is 7. SY samples discussed here are taken stable over a wide range of oxygen fugacity – from (1) Kishon River Mid Reach Multi- as noted above, some of the metamorphic Commodity placer (alluvial samples 982, examples contain Fe3+. In contrast, the SY 1124, 1125, 1174, and 1175), (2) material is associated with native V, which samples 479 and 480 rock samples from requires fO2 at least 8 log units more reducing the Rakefet Magmatic Complex (RMC), than the iron-wustite buffer. This is consistent (3) eluvial sample 767 from the Muhraka with the occurrence of tistarite (Ti2O3) and SiC volcanic body (MHK) and (4) alluvial in the same deposits. sample 751 from the Migdal Ha-Emeq Temperature: Hibonite also is stable over area (map). While the Kishon River Mid a range of temperature. As noted above, the Reach is a narrow gap offering a formation of hibonite in granulite-facies rocks geomorphological and sedimentary trap, appears to occur at temperatures of 700-800 the Migdal HaEmeq area is currently a °C. Hibonite crystallizes from CaO-Al2O3 melts faulted block (Nazareth tilted block) at ca 2100 °C, through a peritectic reaction raising above the proximal reach of the with corundum, but in more SiO2-rich systems Kishon catchment. Neogene volcanics the corundum-hibonite cotectic extends down occur along the faulted margins and to ca 1700 °C. The presence Mg, Ti and F are their relation to SY findings (mainly in expected to lower these liquidus temperatures Mizra River) is being examined. further. 8. Hibonite occurs as rounded grains up to Pressure: There are no independent few mm across, commonly with one or constraints on the pressure of formation for more possible crystal faces. The colour hibonite; it crystallized at very low pressure in in rough tends to be purplish, but in the Solar nebula, at ca 1-2 km depth in the polished grains it commonly is Hatrurim Formation, and at ca 10-30 km depth transparent and has a yellow-orange in the granulite occurrences. The Mt Carmel colour similar to the Myanmar samples probably crystallized at depths gemstones. One characteristic feature is between 30 and 100 km (Griffin et al., 2016). the occurrence of inclusions consisting October, 2016 Page 3 from 9 Pictures of the first hibonite grains that were misidentified as corundum - sample SY-982 Kishon Mid Reach. Top images of the hibonite mounted in epoxy, bottom left image rough grains before mounting (white scale bar =2mm) and bottom right close up of the inclusion from 982-39. These two grains are hibonite intergrown with grossite, fluorite, spinel (large black hexagonal crystals) and native vanadium (small black spherical crystals). Samples: left 1175, right 982, scale bars=500m. October, 2016 Page 4 from 9 This hibonite crystal has native vanadium in dendritic structures. Sample 1124, scale bar right=500 m October, 2016 Page 5 from 9 October, 2016 Page 6 from 9 Shefa Yamim's hibonite findings distribution October, 2016 Page 7 from 9 Samples of Hibonite from various sites in the world Hibonite Mineral , Size: 0.70 x 0.73 x 0.54 cm , Weight: 0.71 g, Origin: Myanmar Photo by kind permission of © www.gemfrance.com www.realgems.org/list_of_gemstones/hibonite.html www.mindat.org/min-1897.html Hibonite Size: 0.45 x 0.43 x 0.32 cm Weight: 0.64 ct Origin: Mogok Area / Myanmar Photo by kind permission of © www.americanthai.com www.realgems.org/list_of_gemstones/hibonite.html October, 2016 Page 8 from 9 References: Griffin, W.L., Gain, S.E.M., Adams, D.T., Thomas Hainschwang, Franck Notari, Laurent Massi, Thomas Armbruster, Benjamin Huang, J-X., Saunders, M., Toledo, V., Rondeau, Emmanuel Fritsch, and Mariko Pearson, N.J.