Protodolomite has been identified in the teeth of Recent echinoids by means of electron microprobe and X-ray diffraction analyses. The analyses demonstrate a high degree of heterogeneity with respect to magnesium carbonate content in these skeletal parts; the entire spectrum of compositions between magnesium calcite and protodolomite was encountered.

AbstractDelindeite and lourenswalsite are two new barium titanosilicate minerals found as microscopic crystals in miarolitic cavities in nepheline syenite in the Diamond Jo quarry, Hot Spring County, Arkansas. Delindeite is found as aggregates of flake-like crystallites in compact spherules, light pinkish grey in colour, with a resinous, pearly lustre. The flakes are biaxial positive with average n ∼ 1.813; the measured density is 3.3 g/cm3. Electron diffraction revealed a monoclinic unit cell in space group C2/m or subgroup, with a = 21.617(13), b = 6.816(5), c = 5.383(3) Å, β = 94.03(5)° (refined from X-ray powder data). The strongest X-ray lines are (hkl, dobs, Irel): (200, 10.80, 100); (311, 3.54, 24); (6̄01, 3.083, 28); (601, 2.888, 31); (2̄21, 2.806, 20); (910, 2.262,18). The crystals are submicroscopically twinned on (100) and also produce additional continuous diffraction streaks parallel to a*, which double the b and c axes. The formula derived from electron and ion probe analyses (H2O by difference), as constrained by density and molar volume data, is approximately (Na,K)2.7(Ba,Ca)4(Ti,Fe,Al)6Si8O26(OH)14, with Na > K, Ba ≫ Ca, Ti ≫ Fe,Al; Z = 1. Lourenswalsite occurs as very thin hexagonal plates in rosettes, silver grey to light brownish grey in colour. The crystals are biaxial negative with very low 2V angle. Indices of refraction are nα = 1.815, nβ ≈ nγ = 1.840; the measured density is 3.17 g/cm = 1.840; the measured density is 3.17 g/cm3. X-ray and electron diffraction show a sharp pseudohexagonal lattice with a = 5.244 Å, but extremely diffuse diffraction streaks normal to the hk0 plane. In these streaks a period of 20.5 Å can be discerned. A hexagonal unit cell with a = 5.244(2) Å, c = 20.49(3) Å can be refined from the powder diffraction data but does not account for some lines, probably because of extreme layer disorder as shown by precession single-crystal patterns. The strong X-ray powder lines are (002, 10.22, 20); (-, 3.93, 20); (111, 2.608, 100); (300, 1.5145, 80); (220, 1.3111, 25). The formula given by microprobe analyses, constrained by density and molar volume data, is approximately (K,Ba)2(Ti,Mg,Ca,Fe)4(Si,Al,Fe)6O14(OH)12 with K > Ba, Ti ≫ (Mg,Ca,Fe), Si > Al > Fe; Z = 1. These minerals are formed under oxidizing weathering conditions, and iron is assumed to be in the Fe3+ state.

Small (<0.5 mm), brownish-pink platy rosettes and yellow spherules, in cavities in nepheline syenite at the Diamond Jo quarry, Magnet Cove, Hot Spring County, Arkansas, have been identified as kassite, CaTirOo(OH)r, a mineral previously known only from the Kola Peninsula, USSR. The Magnet Cove kassite is orthorhombic, in space grotp Ammm, A2mm, A222, or A2,22, with unit-cell parameters a: 12.10, b -- 31.65, c : 4.95 A, and Z: 16; d**: 3.28 g/cm3. Principal X-ray powder lines [d in A, 141 are 7.85(10), 3.26(7), 2.565(7),1.910(8), 1.898(6). The X-ray powder and single-crystal data and density correspond to those reported by earlier workers for cafetite, (Ca,Mg)(Fe,Al)2Ti4Or2'4H2O, from Kola, but the chemical and physical properties correspond to those given in their description of kassite. These earlier workers may have intermixed samples during their Xray study ofkassite and cafetite.

SynopsisThe curious history of the mineral eggonite is reviewed, and two new occurrences are described. The original specimens, for which Schrauf gave good morphological and optical data in 1879, with a tentative suggestion that it was a cadmium silicate, were fakes; the tiny crystals of the new mineral were glued on to hemimorphite specimens from Altenberg, Belgium. In 1929, Zimanyi edited and published observations by Krenner, who found the mineral on silver ores from Felsöbánya, Hungary, added to Schrauf's physical data, and identified it as an aluminium phosphate. It was not until 1959 that Mrose and Wappner showed that it is scandium phosphate, ScPO4 · 2H2O, and essentially identical with kolbeckite, described by Edelmann in 1926 as a phosphate and silicate of beryllium, aluminium, and calcium from Saxony, and with sterrettite, described by Larsen and Montgomery in 1940 as an aluminium phosphate from Fairfield, Utah.In 1980 the IMA Commission on New Minerals and Mineral Names, while accepting the identity of the three minerals and rejecting the name sterrettite, were almost equally divided over the names eggonite and kolbeckite, which are thus both acceptable; since eggonite has 47 years priority, we suggest that it should have preference.The available physical and chemical data on eggonite are summarized and added to, and two new occurrences, at Potash Sulfur Springs, Arkansas, and at Sakpur, Gujarat, India, are described.

________________________ Introduction and acknowledgments ____________ Merumite _________________________ Nature and occurrence -____-________ Previous studies _________________ Chemistry _______________________ Older analyses _____________________ Recent analyses _________________ Isotopic study _________________ X-ray powder data ____________________________ Petrography ________________________ Eskolaite ___________________________________ Occurrence in Finland and Guyana, and (possibly) Siberia ________________________ Chemistry __________________________ Guyanaite __________________________________ Occurrence in Guyana and Finland, and synthesis Chemistry _____________ Analyses ________________________________ Thermal behavior _____________________________ X-ray powder data ____________________ Bracewellite, CrOOH ______________________________ Occurrence and identification ______________ Chemistry _______________________ Analysis ___________________ Page Page 1 Bracewellite, CrOOH Continued 1 Electron-probe study __ __ __ 16 1 X-ray powder data ___________ __ -16 1 Grimaldiite CrOOH and mcconnellite CrOOCu 17 6 Occurrence _______________ ___ 17 7 Physical properties _____ _ __ 18 7 Chemistry _____________ 18 7 Electron-probe analysis _____ -_ _____ _ 19 7 X-ray data __________________ 19 7 Previous syntheses of rhombohedral CrOOH and 8 CrOOCu _________________________ 19 9 Relation of mcconnellite to delafossite 20 y-CrOOH (synthetic) ____________ 21 9 Synthesis _______________ 21 10 X-ray powder data and cell constants _ 22 10 Chromian gahnite ___________________ _ _ 22 10 Properties _____________________-__ 22 11 Electron-probe analysis _______ __ _ 23 11 X-ray data _________________________ 23 12 Other chromian gahnites and zincian chromites _ __ 23 13 Chromian pyrophyllite __________ _ __ _ 24 13 Gold (and silver) in merumite ________ _ _ 24 13 Accessory minerals from Director Creek _ _ 24 15 Crystallographic relationships of CrOOH compounds 28 15 References cited _________________ __ 28