Alumina: (also called aluminum oxide). A compound of two parts aluminum and three parts oxygen which occurs naturally as corundum. Alumina is the base of aluminous salts, a constituent of feldspars, micas, etc.
Topaz is an alumina silicate with a hardness of 8 on the Mohs scale, making it one of the harder gems - but it shares the quality of cleavage with its cousin the diamond.
A silicate of alumina, iron, and magnesia having a bright blue color and vitreous luster.
Iridescence
Reflection of light off internal features in a gem, giving rise to a rainbow like play of colors.
A hard silicate of alumina in rhombic crystals of a colour varying from pink to violet. More rarely, it may be red or green. Its main quality is its exceptional fire.
In each case we used small additions of alumina and zirconia to raise the viscosity of the flux at high temperature.
In the mid1980s, the carbon-magnesite brick became important, and a bit later the alumina-graphite shape.
Prehnite is a hydrous silicate of alumina and lime, with bright, almost luminescent green coloring. It forms thick crusts with a rough or crystalline texture, and is commonly found in cavities and "pillows" along fractures of basalt.
C ORUNDUM is nearly pure alumina (Al2 03), and is found in almost all colors of the rainbow. The transparent varieties rank among the most valuable of gems.
Turquoise rocks are found in arid dry regions where the rocks such as sandstones are heavy with copper deposits and a source of alumina and phosphorus, (volcanic lava). The copper may come from minerals such as malachite, azurite or chrysocolla.
A colourless variety, produced with pure alumina free from potash, correspond to white sapphire and has been called 'Walderite'.
Many cutters use one or more rounds of diamond of varying grades, while others used oxide polish such as alumina to polish tourmaline in one step.
Almandine is an Iron Alumina Garnet, of deep red color, inclining to purple. It is frequently cut with a convex face, or en cabochon, and is then known as carbuncle.
Feldspar: A family of minerals which are all silicates of alumina with either potash, soda, or lime.
yttrium aluminum garnet - an incorrect term for the synthetically grown compound of yttria and alumina. It forms cubic crystals similar to spinel. Its internal structure is like that of garnet, but garnet contains silica not alumina.
Sodalite: An opaque blue-white silicate of alumina and soda with some chlorine, (sodium aluminum silicate and sodium chloride). It looks similar to Lapis, and is a component of Lapis, occurring in massive dodecahedrons and found in igneous rocks.
"In Putnam County, there is a locality of sulphate of alumina and iron, and of sulphate of iron, in Phillipstown, on Anthony's Nose Mountain, about three miles from West Point, at an old iron mine where the ore contains pyrites.
Alumina, cerium oxide, tin oxide, lead, ferric oxide, chromium oxide and silicon oxide etc are few names of the polishing agents used by the gem cutters.
" "A little of everything; there's always flint (silica) and clay (alumina) and magnesia in it and the black is iron, according to its fancy; and there's boracic acid, if you know what that is: and if you don't, ...
CORUNDUM. Crystallised alumina--rubies, sapphire, etc.
CRADLE. Trough in which, by a rocking motion, placer miners wash auriferous or gem gravels.
CRYSTALLOGRAPHY. The science which describes or delineates the form of crystals.
Chemical composition -- Beryllium aluminate.
Optics -- R.I 1.74-1.77, biaxial positive or negative.
Durability -- Hardness 8.5. Chrysoberyl is also exceptionally tough (resistant to breakage), so it produces some extremely durable gems.
It is essentially a silicate of alumina and soda. Scapolite is also called Wernerite, named after the German Geologist A.G. Werner. Scapolite is typically an altered form of plagioclase feldspars found in metamorphic rocks.
Chinastone® - ivory china with alumina added (sometimes incorrectly referred to as stoneware). Patterns include Poppies on Blue™.
Clay - raw material formed when rock breaks down either due to the weather or chemical processes.
The products of the group other than diamonds comprises of Alumina, aluminum and bauxite, borates, coal, copper, diamonds, gold and silver, gypsum, iron ore, molybdenum, salt, sulphuric acid, talc, titanium dioxide, uranium and other products.
Verneuil was asked to replicate the process and he managed to fuse some powdered alumina containing a small amount of chromium with the aid of a oxygen-hydrogen torch. Tiny specimens were the result.
Strontium Titanate (Fabulite), Yttrium Aluminates (YAG), Galliant, Linobate, Djevalite, Zirconia.
Imitations
Various glasses.
Though formal decorative figurines were produced from the 18th century on, the factory's reputation for producing decorative wares only really became established after a bankruptcy in 1884 caused its amalgamation with the Alumina Faience company.
Agate usually occurs as rounded nodules or veins. The layers of quartz are often concentric. The composition of agate varies greatly, but silica is always predominant, usually with alumina and oxide of iron.
The ionic bonds thus formed are much weaker than the ionic-covalent bonds within the silicate and aluminate radicals. Aluminum is not the only element which may bond with oxygen and help to join silicate radicals together.
Comments: The magnesium aluminate mineral spinel is used as a GEM when transparent and finely colored. Ruby colored spinel has been confused with RUBY, the Black Prince's Ruby in the British Imperial State Crown being a famous example.
 See also: Stone, Color, Crystal, Gemstone, Jewel
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