Astrophyllite

ASTROPHYLLITE (from the Greek words "astron" (star) and "phyllon" (leaf) * EN: astrophyllite; DE: Astrophyllit; FR: astrophyllite; ES: astrofilita; RU: астрофиллит) is the rock-forming mineral, titanium-zirconium-silicate (K,Na)3(Mn,Fe)7Ti2[Si4O12]2(O,OH,F)7. The composition is varying. The impurities are: Al2O3 and Fe2O3 (up to several %), ZrO2 (up to 13.6%, namely, zircophyllite), Nb2O5 (up to 6.2%, namely, kupletskite), and also Mg, Li, Rb, Cs (up to 11.6% of Cs2O, namely, cesium-kupletskite). It crystallizes into the triclinic crystal system; the crystal structure is combined, chain-layered. The crystals are thinly-acicular and thinly-tabular, are collected into the spherulites, stellate rosettes (so called "suns"), or entangled-fibrous aggregates. The colour is golden-brown, bronze-yellow, golden-yellow. The hardness is 2-3. The density is 3300-3400 kilograms per cubic metre. It is brittle. It is the characteristical mineral of the nephelinic syenites and their pegmatites. It is the valuable collectible mineral.