Abstract

A third modification of veatchite occurs in Emet colemanite deposit, Kütahya, Turkey, as white cauliflower-shaped nodules associated with colemanite, hydroboracite, realgar, orpi-ment and montmorillonite. The new mineral is triclinic, space group A 1 or A1; a = 20.80, b = 11.72, с = 6.63A (all ±0.3 percent), α = 90°, β = 90°48′, γ = 91°57′ (all ±05′); a:b:c = 1.774:1:0.565; cell volume 1615A3; Z = 4. Density (meas) 2.73, (calc) 2.77 g/cm3. The strongest lines in the X-ray powder photograph and their estimated intensities are: 10.40,100; 3.32,70; 2.59,50; 2.84,20; 3.45,15.

Crystals are transparent, colorless, and well developed and show plate form with rhombic shape. Common forms are {100), {011}, and {O11}. Twin lamellae are parallel to {100}. Cleavage {100} perfect and parallel to dominant plate form, {011} and {011} good; (011)∧(011) ∼60°. Optically biaxial (+), α = 1.549, β = 1.551 (calc), γ = 1.621±0.002 (Na light), 2V = 25°±1°; Z = b, X = c; r< υ strong.

The chemical analysis is (weight percent): SrO 30.88, CaO 0.25, MgO 0.04, B2O3 58.15, H2O(+)9.63, H2O(-)0.15 (total 99.2).

DTA analysis shows endothermic peaks at 455°, 630°, 940°C. Two different phases form at 455° and 630°C.

The new modification is named veatchite-A according to the recommended nomenclature system of polytypes.

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