Andalusite

[Chemical composition] Al can be replaced by Fe ³⁺ (≤96%) and Mn (≤77%).

[Crystal structure] orthorhombic system; a ₀ =0.778 nm, b ₀ =0.792 nm, c ₀ =0.557 nm; Z=2.

[Form] The crystal is columnar and has a nearly regular quadrangle (Fig. G-8). Double crystal is rare, double crystal face (101). When the andalusite captures part of the carbonaceous material and the clay material in the direction of growth, it has a black cross shape in its cross section (Fig. G-9), and the black stripe in the longitudinal section is consistent with the direction in which the crystal extends. This andalusite is called an empty spar. Some andalusite are arranged radially, resembling chrysanthemums, called chrysanthemum stones (Fig. G-10).

Figure G-8 The crystal of andalusite

(quoted from Pan Zhaoyu et al., 1993)

Oblique column: m{110}, n{101}; parallel double-sided: c{001}

(a) (b)

Figure G-9 grit (a) sketch; (b) crystal

Figure G-10 Chrysanthemum stone photo (produced in Xishan, Beijing)

[Physical properties] usually gray, yellow, brown, pink, red or dark green meat (including varieties manganese), as a colorless are rare; glass luster. Cleavage parallel {110} medium. Hardness 6.5 ~ 7.5. The relative density is 3.15 to 3.16.

[Genesis and morphogenesis] Andalusite is mainly a metamorphic mineral. Metamorphism metamorphic region produced at a lower pressure and temperature conditions normally found in aluminum-rich pelitic schist; often cordierite, quartz, white mica, garnet, staurolite, biotite, and other aluminum Mineral symbiosis. Andalusite is also found in the contact zone between argillaceous rocks and intrusive rocks, and is a typical contact metamorphic mineral. The stellite (also known as chrysanthemum stone) of the radial aggregate produced by Xishan chrysanthemum in Beijing is quite famous (Fig. G-10); the contact zone of the Beifangshan rock mass and the muddy surrounding rock in Taipingshan, Beijing, is also seen in contact with metamorphic red. The pillar stone is produced in large quantities.

[identification features] often grayish white, flesh red, columnar crystal form, nearly square cross section, parallel {110} of the two groups of medium cleavage. The empty spar has a unique carbon inclusion. The cobalt nitrate test showed a reaction of Al.

[Main use] It can manufacture advanced refractory materials. Can also be used as raw material for the radome. It can be applied to the ceramic industry to increase the mechanical strength and resistance to rapid cooling and heat. The chrysanthemum-producing rock can be used as decorative stone. Good color, and transparent, coarse grains may as gem materials. Empty spar can be a good ornamental stone.

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