Feldspars (silicates): Sanidine
Diagnostic card.
K Al Si 3 O 8
Singonia monoclinic
Hardness 6-6,5
Specific weight 2.55-2.63
Cleavage is perfect
Break from shell to irregular
Color is colorless, differently colored
Color in powder white
Glitter glass
Sanidine is a stable at high temperatures phase of potassium feldspar. It crystallizes in the form of crystals of prismatic and tabular habit, colorless, transparent and pure, as well as light gray, gray, pinkish and opaque, with glass shine. The powder is always white. Sanidine is a hard and light mineral, easily disintegrating by cleavage along two perpendicular directions.
Chemical composition. Same as orthoclase; In addition, it often contains sodium oxide (Na2O), in which case the chemical formula of the mineral takes the form (K, Na) [AlSi3O8] and it is called kalinatr feldspar or alkali feldspar. The shape of the crystals. Tablite vkapadenniki in effusive rocks (rhyolites, trachytes, phonolites). Crystal structure. Silicate with an infinite three-dimensional frame (SiAl) O4. Class of symmetry. Prismatic - 2 / m. Cleavage. Perfect in the basis (P), perfect along the side faces (M) and along the prism (T) (see feldspars). Aggregates. Dense, granular.
Diagnostic signs.
Does not melt and can not be acted upon by ordinary acids; Only fluoric acid completely decomposes it. Melts with difficulty. Behavior in acids. Almost does not dissolve.
Origin.
Sanidine is of considerable scientific interest as a mineral, characteristic primarily for effusive rocks of geologically young age, which are of the trachyte type. In addition, it acts as a mineral that forms part of many plutonic and metamorphic rocks.
Place of Birth.
In Italy it is a fairly common mineral, sometimes forming relatively large crystals. Smaller crystals form a vein in a pumice stone in Pitigliano (Grosseto province) and fill the voids in the lavas of Vesuvius and the islands of Ustica and Pantelleria.
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