Rubies

Corundum is a relatively hard mineral, coming in at a nine on the Mohs gemstone hardness scale. This quality could certainly contribute to its popularity in the world of jewelry, as the hardness of the gemstone lends itself to use in a variety of interesting and beautiful fine jewelry styles and settings.

The corundum family of gemstones consists of ruby and sapphire. Corundum is very compact, dense, and lacks gemstone cleavage. It’s also the second hardest natural mineral after diamond. These factors make both varieties of corundum some of the most highly desired jewelry stones. Ruby is the red variety of corundum.

In addition to its use as a precious gem, corundum finds some use as an abrasive, owing to the extreme hardness of the material (9 on the Mohs hardness scale). It is used for grinding optical glass and for polishing metals and has also been made into sandpapers and grinding wheels.

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.

: a very hard mineral that consists of aluminum oxide occurring in massive and crystalline forms, that can be synthesized, and that is used for gemstones (such as ruby and sapphire) and as an abrasive.

A diamond is much harder than corundum, even though they’re only one division apart on the scale. The Mohs scale starts approximately linear, but the curve climbs sharply at the high end. Corundum (9) is twice as hard as topaz (8), and diamond (10) is four times as hard as corundum.

Melt Processes The most inexpensive and oldest melt process is known as flame fusion. In this method, a flame melts aluminum oxide powder (the principal mineral in corundum).

amethyst, a transparent, coarse-grained variety of the silica mineral quartz that is valued as a semiprecious gem for its violet colour. In ancient writings the Latin name amethystus was used for amethyst, purple corundum, and purple garnet. …

What is another word for corundum?

is that corundum is (mineral) an extremely hard mineral, a form of aluminum oxide with the chemical formula al]]2[[oxygen|o3, that occurs in the form of the gemstones sapphire and ruby; it is used as an abrasive while emerald is any of various green gemstones, especially a green transparent form of beryl, highly valued …

Star corundum gemstones show asterism, or a “star effect.” This phenomenon is created by the inclusion of rutile needles within the host corundum crystal. The rutile needles orient themselves according to the hexagonal symmetry of the corundum, and reflections from these needles provide a chatoyancy.

Gem-quality corundum is also quite rare. These factors make both varieties of corundum some of the most highly desired jewelry stones. Ruby is the red variety of corundum. All other colors of corundum, including colorless, are called sapphires.

Very rarely there are two distinct sets of needles oriented according to the first and second order prisms of the corundum (30° apart), resulting in a strong, 12-rayed star. For more information on corundum inclusions, see Identifying Origins of Rubies and Sapphires.

Gem-quality corundum is often found in placer deposits. Non-gem corundum is abundant throughout the world. Inclusions. In general, Burmese, Thai, and Australian blue sapphires contain crystals of plagioclase feldspars, orthoclase, niobite, columbite, calcite, monazite, zircon, apatite, fergusonite, and thorite.