Basal pinacoid

TOPAZ. The mineral topaz is a silicate of aluminum and fluonne corresponding to the formula A SiO F, OTT)2. It is orthorhombic and its crystals are mostly prismatic terminated by pyramidal and odier faces, the basal pinacoid being often present, Massive varieties are known. It has an easy and perfect basal cleavage, hence for this reason gems or fine specimens should be handled with care to avoid developing cleavage... 

For the micas, the most frequent simple forms in the orientation of Kokscharov are, according to the Naumann s notation, the basal pinacoid c is oP, the lateral pinacoid b is yPy, the prism M is 2P and the prism o is P. 

Alite crystals, granular, showing strong growth perpendicular to basal pinacoid (0001) due to development of pyramidal faces solely variety concomitant increase in belite size Recrystallization of alite during retention for 120 min at 1600°C melt is low in degree of supersaturation (Maki, Haba, and Takahashi, 1983)... 

Small, thin crystals of alite, developing on basal pinacoid (0001) Rapid crystallization (Ono, Kawamura, and Soda, 1968)... 

Basal pinacoids and prisms with crystals flattened parallel to the basal pinacoids... 

Subsequently, another distinction was made for the "biaxial" micas, once it was clarified (see below) that they belong to the monoclinic system with the plane of symmetry normal to the cleavage lamina as started by Rensch in 1869. The plane of the optic axes could be normal or parallel to the plane of symmetry observed in crystals having the lateral pinacoid 010 well developed. These micas were called, respectively, type I and type II. Actually, this different behavior had been observed by Silliman in as early 1850. He wrote of a short and long diagonal of the basal face. 

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