American Mineralogist, Volume 69, pages 374-376, 1984
Tinsleyite,the aluminum analog* from theTip Toppegmatite in $"t".rffff"1Tgnite,
PBrr J. DUNN Department of Mineral Sciences Smithsonian Institation, Washington, D.C. 20560
Ror-eND C. RousB Department of Geological Sciences University of Michigan, Ann Arbor, Michigan 48109
THoues J. CeMpsnLL AND WtI-leno L. Rosnnrs Museum of Geology South Dakota School of Mines and Technology Rapid City, South Dakota 57701
Abstract
Tinsleyite, KAI2@O4)2(OH). 2H2O, is a new speciesfrom the Tip Top Mine, near Custer, South Dakota. It is monoclinic,space group Pnor PZln, with a : 9.602(8),b = 9.532(6),c : 9.543(ll)4, p = 103.16(6)",and Z :4. The strongestpowder diffractionlines are (d, I, hkt):6.68,10,n0,011;5.91,8,101,TI1;3.006,7,130,031.T13:2.616.6,$2.231, 132,320.Microprobe analysisyields K2O 12.4,Fe2O3 5.2, MnzOr Ll, Al2O326.6, P2O5 42.2,H1O (by difference)12.5, sum : 100.0weight percent. Tinsleyiteis dark magentared, with pink streak,hardness (Mohs) approximately5, and density 2.69 (meas.), 2.62 (caIc.) g/cm3.The luster is vitreous. Optically, tinsleyite is biaxial,positive,2V=S6",withindicesofrefractiona:1.591,8:1.597, y:1.604. Itis strongly pleochroic with X = pale orange brown, I : light purple, and Z = dark purplish red; absorption: Z > Y > X, X : b. Tinsleyite is associatedwith leucophosphite, rockbridgeite, tavorite, carbonate-apatite,and robertsite in highly altered triphylite pods in the pegmatite. Tinsleyite is chemically the Al-analogue of leucophosphitebut apparently differs slightly in structure. Type material is depositedin the SmithsonianInstitution under #159882.Tinsleyite is named in honor of Mr. Frank C. Tinsley of Rapid City, South Dakota.
Introduction Dakota. As a direct result of his efforts, much valuable As part of a study of the mineralogy of the Tip Top research material has been saved from loss or destruc- pegmatiteby one ofthe authors(TJC), several leucophos- tion. The species and the name were approved by the Names. phite samples of unusual appearance were studied in IMA Commissionon New Mineralsand Mineral detail. One of these, a magenta-colored material, first Type material is preserved at the SmithsonianInstitution found in the late 1960's, was found to contain abundant and in the private collection of WLR. Al. Our subsequentstudy has shown that these magenta- colored crystals are in part a new mineral, the Al- Physical and optical properties analogue of leucophosphite. Additional material was Tinsleyite occurs as thin, magenta-redlayers on com- found in 1982and some of this was found to be the new mon Fe-rich leucophosphite with parting surfaces be- phaseusing optical methods. tweenthe two species.Tinsleyite forms as the outermost We take pleasure in naming this mineral tinsleyite in zone of such composite crystals and approaches the honor of Mr. Frank C. Tinsley of Rapid City, South composition given herein only in the 0.05 mm outer Dakota. Mr. Tinsley has been a long-term contributor to portions of the crystals. The streak is pink and the the preservation of rare and unusual specimensfrom the hardnessis approximately 5 (Mohs). The luster is vitre- Tip Top pegmatite and many other localities in South - ous on crystal faces and fracture surfaces.The density of 0003-004)o8410304-0374$02.00 374 DUNN ET AL.: TINSLEYITE 375 the outermost, most Al-rich, zone of tinsleyite is 2.69(5) g/cm3, as determined using heavy liquid methods. This comp€rreswell with the calculated density of 2.62 glcm3. There is no visible fluorescencein ultraviolet radiation. Tinsleyite is brittle. The red color of tinsleyite (and some associatedleucophosphite) is ascribedto trivalent manga- nese,as noted under "Chemistry." Tinsleyite is biaxial, positive, 2V : 86" (measuredand calculated),with indices of refraction a : 1.591,B = 1.597,and, y : 1.604(all t0.003). Tinsleyiteis strongly pleochroic with X : pale orange-brown, I = light purple, and,Z = dark purplish red; absorption is Z > Y > X and the orientation is X ll b. Dispersion is indiscernible due to the intensepleochroism. Color zoning is apparentin most crystals examined. Calculation of the Gladstone-Dale relationship using the constants of Mandarino (1981) Fig. l. Tinsleyitecrystal from Tip Top pegmatite.The large yields Ks = 0.216for the chemical composition and K" = crystalface is (l0l). 0.222, indicating excellent compatibility of the chemical and physical data. The above description applies to the holotype material, basisof theprimitive cell describedbelow, are 1TOt1, 1Tt t), and it must be emphasized that not all the magenta- {011},and {110}.Tinsleyite crystals are tabular on {T0l}. colored material examined was tinsleyite. Some of the An SEM micrograph of a representativecrystal is shown material was essentially pure leucophosphite with only in Figure l. traces of Al, and the dark red color of tinsleyite is, The crystal fragment chosen for X-ray study was a therefore, not a useful diagnostic property. Optical ex- composite (as were a// fragments), consisting of a color- amination, emphasizingindices of refraction, and X-ray less leucophosphite core enveloped by magenta-colored powder difraction data are the most reliable means for tinsleyite. Precessionphotographs taken with MoKa and the difierentiation of these two closely-related speciesin CuKa radiations showed two, nearly coincident, primi- thosecases where chemicalanalysis is not possible. tive monoclinic lattices. -One had cell parameters d = 9.77,b:9.65,c:9.754, andB: 103.4",which agree Chemistry within 0.014 with those reported by Moore (1972) for leucophosphitefrom the Tip Top mine. There is also a Tinsleyite was chemically analyzed using an ARL-SEMe close correspondenceto the cells ofthe Brazilian material electron microprobe utilizing an operating voltage of 15 (Lindberg, 1957)and synthetic leucophosphite(Smith and kV and a samplecurrent of 0.025g,A, measuredon brass. Brown, 1959).The secondlattice had cell parameters0.1 The standardsused were microcline (K), montgomeryite to 0.24 less than those of the first and is ascribed to (P,Al), manganite(Mn), and maricite (Fe). The data were tinsleyite. Their refined values, which were derived from corrected using standard Bence-Albee factors. A wave- the powder difraction data (Table l) using least-squares length-dispersivemicroprobe scan indicated the absence and an NBS silicon internal standard(a = 5.43088A),are of other elementswith atomic number greater than 8. The a:9.ffi2(8), b:9.532(6), c:9.543(ll)4, and = resultant analysisis: K2O 12.4, Fe2O35.2, Mn2O3,l.l, B 103.16(6)".Tinsleyite reflections were slightly out-of- Al2O326,6,P2Os42.2, HzO (by difference): 12.5,sum : focus on the precession photographs. This indicates a 1fi).0percent. Mn is assumedto be Mn3+ becauseof the slight difference in orientation of the two speciesin the intimate association with robertsite and the dark red composite crystals, which may be regarded as epitaxial color, which is consistent with the absorption of Mn3* in overgrowths of tinsleyite on leucophosphite. the visible range. Water was calculated by difference The space group of tinsleyite is Pn or P2ln, which becauseof extreme paucity of material; the validity of differs from that of leucophosphite (P4ln) in its lack of this assumptionis supported by the known crystal struc- screwaxes. This is proven by the presenceofa weak 010 tural formula of leucophosphite (Moore, 1972).Calcula- reflection on the CuKa precessionphotographs, the other tion of the chemical formula of tinsleyite, basedon P : 2, odd orders along b* being absent. As the powder data yields: K0Ee(Alr.75Fe3lrrIUnair)rr.02(PO4)2(OH)0e5. (Table 1) also contain a weak but distinct line at 9.594. l.86H2Oor, ideally, KA12@O4)2(OH). 2H2O withZ: 4. which can only be indexed as 010 (d"a. : 9.534), the precessionspot cannot be dismissedas an extraneousre- Crystallography flection due to multiple difraction or anode contamina- Tinsleyite occurs as monoclinic crystals of tabular tion. None of the published powder data for leucophos- prismatic habit essentially identical to that of leucophos- phite contains this line and an examination of all phite (Lindberg, 1957).The forms present, indexed on the leucophosphitepowder photographs in the Smithsonian 376 DUNN ET AL.: TINSLEYITE
Table l X-ray powder diffraction data for tinsleyite Occurrence Tinsleyite occurs in the Tip Top pegmatite,located just oobs ocal hkl dobs cca hkl c lc southwestof the center of Section 8, T4S, R4E, approxi- mately 5.5 miles southeastof Custer, South Dakota. I 9.59 9.53 0l0 <