--quartz

Β- quartz is stable at 573-870 °C under normal pressure, and becomes tridymite when the temperature is high. When the temperature is less than 573 °C, the displacement is converted to α-quartz. Most of the beta quartz now seen has been converted into alpha quartz, but still retains the hexagonal double cone state of the beta quartz (called a secondary image).

[Crystal Structure] Hexagonal System, a ₀ = 0.502 nm, c ₀ = 0.548 nm, Z = 3. The structure is obtained by shifting the [SiO ₄ ] tetrahedron in the α-quartz structure to change the cubic helix axis in the structure to the sixth-order helical axis.

[Form] The development of hexagonal double cone {1011}, sometimes visible small hexagonal column {1010}.

[Physical properties] Beta quartz is usually grayish white, milky white; glass luster, broken grease luster. No clerk. Hardness 6.5 to 7. The relative density is 2.53. It is converted to α-quartz under normal temperature and pressure, and the relative density is increased to 2.65.

[Cause and occurrence] Acidic effluent is porphyry, or found in the crystal cavity, which is a direct crystallization product, which has been converted into α-quartz, but is made into a sub-image according to β-quartz (Fig. Y-20).

Figure Y-20 Hexagonal double-cone crystal form of β-quartz, but usually has been converted to α-quartz and still retains the secondary image of β-quartz hexagonal double-cone