What is the crystal structure of corundum?
What is the crystal structure of corundum?
Crystals of corundum are commonly well formed, often rather large, showing hexagonal and rectangular sections. Crystals are commonly bounded by hexagonal prisms or steep hexagonal di-pyramids resulting in barrel-shaped forms. Tabular and rhombohedral forms are also found, but much less common.
What is the characteristics of corundum?
Corundum is an aluminum oxide that commonly forms hexagonal barrel-shaped prisms that taper at both ends or as thin tabular hexagonal plates. It has a hardness of 9 on the Mohs scale, making it one of the most durable commercial gemstones. It has no dominant cleavage and fractures in a conchoidal manner.
What color is corundum stone?
| Corundum | |
|---|---|
| Color | Colorless, gray, golden-brown, brown; purple, pink to red, orange, yellow, green, blue, violet; may be color zoned, asteriated mainly grey and brown |
| Crystal habit | Steep bipyramidal, tabular, prismatic, rhombohedral crystals, massive or granular |
| Twinning | Polysynthetic twinning common |
What gems are corundum?
Corundum, naturally occurring aluminum oxide mineral (Al2O3) that is, after diamond, the hardest known natural substance. Its finer varieties are the gemstones sapphire and ruby (qq. v.), and its mixtures with iron oxides and other minerals are called emery (q.v.).
How is the crystal structure of corundum determined?
a mineral, a natural anhydrous alumina, Al 2 O 3. Corundum crystallizes in the trigonal system. Its crystal structure consists of aluminum atoms surrounded by six oxygen atoms, which form a highly dense hexagonal packing. The oxygen layers are located parallel to the (0001) face of corundum.
What kind of crystal is corundum al 2O 3?
Corundum, Al 2O 3 (aluminum = silver; oxygen = red). A hexagonal (rhombohedral) crystal system constructed of aluminum atoms that are each surrounded by six oxygen atoms. The oxygen atoms are not bonded at the corners of a regular octahedron. Hematite model, side view.
Which is a black massive variety of corundum?
Emery: A black massive variety of corundum. Colour is caused by a mixture of magnetite, hematite and spinel. In 1876, a girl named Annie and her father Henry Robillard discovered a mass deposit of corundum in a mountainous area.
What is the difference between clear and opaque corundum?
The clear varieties are used as gems and the opaque as abrasive materials. Corundum occurs in crystals of the hexagonal system and in masses. It is transparent to opaque and has a vitreous to adamantine luster. The transparent gem varieties are colorless, pink, red, blue, green, yellow, and violet; the common varieties are blue-gray to brown.