What is a cross stone?

The cross stone is an island-like structure of silicate minerals, which is named for its unique cross shape. The cross stone is hard and brittle, with a dull sheen, usually dark brown. A rare transparent cross stone can be used as a gemstone. Because of its shape, people often use it to make ornaments.

Cross stone

Chemical composition: Fe2Al9[SiO4]4O7(OH)2. Equivalent to two kyanite plus iron hydroxide.

Crystal structure: orthorhombic system, a = 0.781 nm, b = 0.1662 nm, c = 0.565 nm. Z=2, the crystal structure can be regarded as a parallel (010) plane kyanite structure layer, which has been superposed on each other with iron hydroxide, which makes the (100) plane of kyanite according to the cross stone (010) Face into a rule.

Physical properties: brown red, reddish brown, light yellow brown or black, glass luster, dull or dull when impure, translucent - opaque. Photometric: biaxial crystal, positive light. Fluorescence: Fluorescent inertness under UV light. Absorption spectrum: sometimes strong absorption line near 450 nm, weak absorption line near 580 nm. {010}The cleavage is medium, and the difference is to the shell-like fracture. The Mohs hardness is 7.5, the relative density is 3.74~3.83g/cm?, the crystal is usually coarse and short columnar, and the cross shape is common through the double crystal, hence the name.

Origin: Brazil, Switzerland, the United States.

Occurrence: mainly the product of regional metamorphism and a few contact metamorphism.

Identification features: short columnar shape, cross section is diamond shape. Especially the twin crystal shape, dark brown, reddish brown, and high hardness, which is different from the andalusite.

Cruciite is a product of regional metamorphism of iron-rich and aluminum-rich argillaceous rocks. It is found in mica schist, phyllite and gneiss. It is a mineral of intermediate metamorphism. The cross stone is occasionally transparent and can be used as a gemstone.

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