"produce aluminium metal, as an abrasive owing to its hardness, and as a refractory material owing to its high melting point. Corundum is the most common naturally occurring crystalline form of aluminium oxide. Rubies and sapphires are gem-quality forms of corundum, which owe their characteristic colors to trace impurities. Rubies are given their characteristic deep red color and their laser qualities by traces of chromium. Sapphires come in different colors given by various other impurities, such as iron and titanium. AlO is an electrical insulator but has a relatively high thermal conductivity () for a ceramic material. Aluminium oxide is"
"10.0 and moissanite falling somewhere in between corundum (ruby) and diamond in hardness. Sapphire, ruby, and pure corundum are α-alumina, the most stable form of AlO, in which 3 electrons leave each aluminum ion to join the regular octahedral group of six nearby O ions; in pure corundum this leaves all of the aluminum ions with a very stable configuration of no unpaired electrons or unfilled energy levels, and the crystal is perfectly colorless. When a chromium atom replaces an occasional aluminum atom, it too loses 3 electrons to become a chromium ion to maintain the charge balance of the"
"Dome Rock Mountains of La Paz County, Arizona, Stockdale, Riley County, Kansas; Cortlandt, New York; and Clay County, North Carolina. Sapphirine Sapphirine is a rare mineral, a silicate of magnesium and aluminium with the chemical formula (Mg,Al)(Al,Si)O (with iron as a major impurity). Named for its sapphire-like colour, sapphirine is primarily of interest to researchers and collectors: well-formed crystals are treasured and occasionally cut into gemstones. Sapphirine has also been synthesized for experimental purposes via a hydrothermal process. Typical colours range from light to dark sapphire blue, bluish to brownish green, green, and bluish or greenish gray to black; less"
"Sapphirine Sapphirine is a rare mineral, a silicate of magnesium and aluminium with the chemical formula (Mg,Al)(Al,Si)O (with iron as a major impurity). Named for its sapphire-like colour, sapphirine is primarily of interest to researchers and collectors: well-formed crystals are treasured and occasionally cut into gemstones. Sapphirine has also been synthesized for experimental purposes via a hydrothermal process. Typical colours range from light to dark sapphire blue, bluish to brownish green, green, and bluish or greenish gray to black; less common colours include yellow, pale red, and pink to purplish pink. Sapphirine is relatively hard (7.5 on Mohs scale), usually"
"only in ruby. Sapphire and ruby are both varieties of the same mineral; corundum. Some minerals may replace other existing minerals while preserving the original's habit: this process is called pseudomorphous replacement. A classic example is tiger's eye quartz, crocidolite asbestos replaced by silica. While quartz typically forms ""prismatic"" (elongate, prism-like) crystals, in tiger's eye the original ""fibrous"" habit of crocidolite is preserved. The names of crystal habits are derived from: Predominant crystal faces (prism – prismatic, pyramid – pyramidal and pinacoid – platy). Crystal forms (cubic, octahedral, dodecahedral). Aggregation of crystals or aggregates (fibrous, botryoidal, radiating, massive). Crystal appearance"
"glassmaking and also as a glaze for ceramics. Green chromium oxide is extremely lightfast and as such is used in cladding coatings. It is also the main ingredient in infrared reflecting paints, used by the armed forces to paint vehicles and to give them the same infrared reflectance as green leaves. Natural rubies are corundum (aluminum oxide) crystals that are colored red (the rarest type) due to chromium (III) ions (other colors of corundum gems are termed sapphires). A red-colored artificial ruby may also be achieved by doping chromium(III) into artificial corundum crystals, thus making chromium a requirement for making"
"AlO crystal. However, the Cr ions are larger and have electron orbitals in different directions than aluminum. The octahedral arrangement of the O ions is distorted, and the energy levels of the different orbitals of those Cr ions are slightly altered because of the directions to the O ions. Those energy differences correspond to absorption in the ultraviolet, violet, and yellow-green regions of the spectrum. If one percent of the aluminum ions are replaced by chromium in ruby, the yellow-green absorption results in a red color for the gem. Additionally, absorption at any of the above wavelengths stimulates fluorescent emission"
"2.38% aluminium by mass. Because of its strong affinity for oxygen, aluminium is almost never found in the elemental state; instead it is found in oxides or silicates. Feldspars, the most common group of minerals in the Earth's crust, are aluminosilicates. Aluminium also occurs in the minerals beryl, cryolite, garnet, spinel, and turquoise. Impurities in AlO, such as chromium and iron, yield the gemstones ruby and sapphire, respectively. Native aluminium metal can only be found as a minor phase in low oxygen fugacity environments, such as the interiors of certain volcanoes. Native aluminium has been reported in cold seeps in"
"specimens will be intermediate between them. Pleochroism may be extreme, with trichroic colours ranging from: colourless, pale yellow or red; sky to lavender blue, or bluish-green; to dark blue. There is no reaction under ultraviolet light. While there is evidence of magmatic origin in some deposits, sapphirine is primarily a product of high grade metamorphism in environments poor in silica and rich in magnesium and aluminium. However, sapphirine occurs in a variety of rocks, including granulite and amphibolite facies, calc-silicate skarns, and quartzites; it is also known from xenoliths. Associated minerals include: calcite, chrysoberyl, cordierite, corundum, garnet, kornerupine, kyanite, phlogopite,"
"Aluminium hydroxide Aluminium hydroxide, Al(OH), is found in nature as the mineral gibbsite (also known as hydrargillite) and its three much rarer polymorphs: bayerite, doyleite, and nordstrandite. Aluminium hydroxide is amphoteric in nature, i.e., it has both basic and acidic properties. Closely related are aluminium oxide hydroxide, AlO(OH), and aluminium oxide or alumina (AlO), the latter of which is also amphoteric. These compounds together are the major components of the aluminium ore bauxite. The naming for the different forms of aluminium hydroxide is ambiguous and there is no universal standard. All four polymorphs have a chemical composition of aluminium trihydroxide"
"Aluminium Aluminium or aluminum is a chemical element with symbol Al and atomic number 13. It is a silvery-white, soft, nonmagnetic and ductile metal in the boron group. By mass, aluminium makes up about 8% of the Earth's crust; it is the third most abundant element after oxygen and silicon and the most abundant metal in the crust, though it is less common in the mantle below. The chief ore of aluminium is bauxite. Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments. Instead, it is found combined in over 270 different"
"(being the most common of the gem garnets). Almandine occurs in metamorphic rocks like mica schists, associated with minerals such as staurolite, kyanite, andalusite, and others. Almandine has nicknames of Oriental garnet, almandine ruby, and carbuncle. Pyrope (from the Greek ""pyrōpós"" meaning ""fire-eyed"") is red in color and chemically an aluminium silicate with the formula MgAl(SiO), though the magnesium can be replaced in part by calcium and ferrous iron. The color of pyrope varies from deep red to black. Pyrope and spessartine gemstones have been recovered from the Sloan diamondiferous kimberlites in Colorado, from the Bishop Conglomerate and in a"
"wasn't until 1783 that spinels were differentiated from rubies. The two gemstones can be distinguished on the basis of their chemical properties: a red spinel is a compound of magnesia, iron, oxygen, and chromium, while a ruby is a type of aluminium oxide. The rarity of this spinel, however, is that it is the biggest uncut spinel in the world, given that it has only been polished slightly, and has never received a proper cut, gemologically speaking. The Black Prince's Ruby enters the ""stage of history"" in middle of the 14th century as the possession of Abū Sa'īd, the Arab"
"Peru, Poland, Russia and Sri Lanka. Dumortierite Dumortierite is a fibrous variably colored aluminium boro-silicate mineral, AlBO(SiO)O. Dumortierite crystallizes in the orthorhombic system typically forming fibrous aggregates of slender prismatic crystals. The crystals are vitreous and vary in color from brown, blue, and green to more rare violet and pink. Substitution of iron and other tri-valent elements for aluminium result in the color variations. It has a Mohs hardness of 7 and a specific gravity of 3.3 to 3.4. Crystals show pleochroism from red to blue to violet. ""Dumortierite quartz"" is blue colored quartz containing abundant dumortierite inclusions. Dumortierite was"
"of a gemstone, we speak of primary and secondary and sometimes tertiary hues. Ruby is defined to be red. All other hues of the gem species corundum are called sapphire. Ruby may exhibit a range of secondary hues, including orange, purple, violet, and pink. Improving the quality of gemstones by treating them is common practice. Some treatments are used in almost all cases and are therefore considered acceptable. During the late 1990s, a large supply of low-cost materials caused a sudden surge in supply of heat-treated rubies, leading to a downward pressure on ruby prices. Improvements used include color alteration,"
"epsomite, potash alum, melanterite and gypsum. The crystallochemical formula, can be written as: [Al(HO)](SO)5HO. The second formula shows that HO in the alunogen formula occurs both as ligand (coordinative form) and loosely bound (crystallization) form. Alunogen Alunogen (from French ""alun"", “alum”), also called feather alum and hair salt is a colourless to white (although often coloured by impurities, such as iron substituting for aluminium) fibrous to needle-like aluminium sulfate mineral. It has the chemical formula Al(SO)·17HO. It is often found on the walls of mines and quarries as a secondary mineral. It can be found in the oxidation zones of"
"Topaz Topaz is a silicate mineral of aluminium and fluorine with the chemical formula AlSiO(F, OH). Topaz crystallizes in the orthorhombic system, and its crystals are mostly prismatic terminated by pyramidal and other faces. It is one of the hardest naturally occurring minerals (Mohs hardness of 8) and is the hardest of any silicate mineral. This hardness combined with its usual transparency and variety of colors means that it has acquired wide use in jewellery as a cut gemstone as well as for intaglios and other gemstone carvings. Topaz in its natural state is a golden brown to yellow, a"
"several forms (polymorphs). Nitrides of silicon and phosphorus are also known, but only the former is commercially important. The nitrides of aluminium, gallium, and indium adopt diamond-like wurtzite structure in which each atom occupies tetrahedral sites. For example, in aluminium nitride, each aluminium atom has four neighboring nitrogen atoms at the corners of a tetrahedron and similarly each nitrogen atom has four neighboring aluminium atoms at the corners of a tetrahedron. This structure is like hexagonal diamond (lonsdaleite) where every carbon atom occupies a tetrahedral site (however wurtzite differs from sphalerite and diamond in the relative orientation of tetrahedra). Thallium(I)"
"the range 2.67 to 2.69, but Webmineral has 2.4 to 2.66. Chalcophyllite is soluble in acids and in ammonia. It is not fluorescent, nor radioactive. The water content varies at room temperature based on relative humidity. Chalcophyllite alters to chrysocolla, which is a copper-aluminium silicate with the formula (Cu,Al)HSiO(OH)·n(HO). Many copper minerals are blue or green in color; chalcophyllite is blue-green to emerald-green, with a pale green streak and vitreous to subadamantine luster, pearly on {0001}. Crystals are transparent to translucent. It is uniaxial (-) with refractive indices n = 1.618 to 1.632 and n = 1.552 to 1.575. Indices"
"Spinel Spinel () is the magnesium aluminium member of the larger spinel group of minerals. It has the formula MgAlO in the cubic crystal system. Its name comes from Latin ""spina"" (arrow). Balas ruby is an old name for a rose-tinted variety of spinel. Spinel crystallizes in the isometric system; common crystal forms are octahedra, usually twinned. It has an imperfect octahedral cleavage and a conchoidal fracture. Its hardness is 8, its specific gravity is 3.5–4.1, and it is transparent to opaque with a vitreous to dull luster. It may be colorless, but is usually various shades of pink, rose,"
"Ammonium iron(III) sulfate Ammonium iron(III) sulfate, NHFe(SO)·12 HO, or NH[Fe(HO)](SO)·6 HO, also known as ferric ammonium sulfate (FAS) or iron alum, is a double salt in the class of alums, which consists of compounds with the general formula AB(SO) · 12 HO. It has the appearance of weakly violet, octahedrical crystals. There has been some discussion regarding the origin of the crystals' colour, with some ascribing it to impurities in the compound, and others claiming it to be a property of the crystal itself. FAS is paramagnetic, acidic and toxic towards microorganisms. It is a weak oxidizing agent, capable of"
"Aluminium phosphide Aluminium phosphide (aluminum phosphide) is a highly toxic inorganic compound with the chemical formula used as a wide band gap semiconductor and a fumigant. This colorless solid is generally sold as a grey-green-yellow powder due to the presence of impurities arising from hydrolysis and oxidation. AlP crystals are dark grey to dark yellow in color and have a zincblende crystal structure with a lattice constant of 5.4510 Å at 300 K. They are thermodynamically stable up to . Aluminium phosphide reacts with water or acids to release phosphine: AlP is synthesized by combination of the elements: Caution must"
"ore of titanium; other examples include cassiterite (SnO; ore of tin), and pyrolusite (MnO; ore of manganese). In hydroxides, the dominant anion is the hydroxyl ion, OH. Bauxites are the chief aluminium ore, and are a heterogeneous mixture of the hydroxide minerals diaspore, gibbsite, and bohmite; they form in areas with a very high rate of chemical weathering (mainly tropical conditions). Finally, multiple oxides are compounds of two metals with oxygen. A major group within this class are the spinels, with a general formula of XYO. Examples of species include spinel (MgAlO), chromite (FeCrO), and magnetite (FeO). The latter is"
"Kelley of ICT, Inc. also developed a variant of the Czochralski process where natural ruby is used as the 'feed' material. One of the most crucial factors in successfully crystallising an artificial gemstone is obtaining highly pure starting material, with at least 99.9995% purity. In the case of manufacturing rubies or sapphires, this material is alumina. The presence of sodium impurities is especially undesirable, as it makes the crystal opaque. Depending on the desired colouration of the crystal, small quantities of various oxides are added, such as chromium oxide for a red ruby, or ferric oxide and titania for a"
"ones, which are called rubies. The term ""Yogo sapphire"" refers only to sapphires from the Yogo Gulch. The cornflower blue color of the Yogo results from trace amounts of iron and titanium. Yogo sapphires are unique in that they are free of cavities and inclusions, have high uniform clarity, lack color zoning, and do not need heat treating because their cornflower blue coloring is uniform and deep. Unlike Asian sapphires, they maintain their brilliance in artificial light. Yogos present an advantage to gemcutters: since they are found as primary constituent minerals within an igneous bedrock rather than in sedimentary alluvial"
"(and not for the German geologist Johannes Böhm (1857–1938) as often stated). Boehmite Boehmite or böhmite is an aluminium oxide hydroxide (γ-AlO(OH)) mineral, a component of the aluminium ore bauxite. It is dimorphous with diaspore. It crystallizes in the orthorhombic dipyramidal system and is typically massive in habit. It is white with tints of yellow, green, brown or red due to impurities. It has a vitreous to pearly luster, a Mohs hardness of 3 to 3.5 and a specific gravity of 3.00 to 3.07. It is colorless in thin section, optically biaxial positive with refractive indices of nα = 1.644"
"Dumortierite Dumortierite is a fibrous variably colored aluminium boro-silicate mineral, AlBO(SiO)O. Dumortierite crystallizes in the orthorhombic system typically forming fibrous aggregates of slender prismatic crystals. The crystals are vitreous and vary in color from brown, blue, and green to more rare violet and pink. Substitution of iron and other tri-valent elements for aluminium result in the color variations. It has a Mohs hardness of 7 and a specific gravity of 3.3 to 3.4. Crystals show pleochroism from red to blue to violet. ""Dumortierite quartz"" is blue colored quartz containing abundant dumortierite inclusions. Dumortierite was first described in 1881 for an"
"Orpiment Orpiment is a deep orange-yellow colored arsenic sulfide mineral with formula . It is found in volcanic fumaroles, low temperature hydrothermal veins, and hot springs and is formed both by sublimation and as a byproduct of the decay of another arsenic mineral, realgar. It takes its name from the Latin ""auripigmentum"" (""aurum"" − gold + ""pigmentum"" − pigment) because of its deep-yellow color. Orpiment was traded in the Roman Empire and was used as a medicine in China even though it is very toxic. It has been used as a fly poison and to tip arrows with poison. Because"
"Rubidium oxide Rubidium oxide is the chemical compound with the formula RbO. Rubidium oxide is highly reactive towards water, and therefore it would not be expected to occur naturally. The rubidium content in minerals is often calculated and quoted in terms of RbO. In reality, the rubidium is typically present as a component of (actually, an impurity in) silicate or aluminosilicate. A major source of rubidium is lepidolite, KLiAl(Al,Si)O(F,OH), wherein Rb sometimes replaces K. RbO is a yellow colored solid. The related species NaO, KO, and CsO are colorless, pale-yellow, and orange, respectively. The alkali metal oxides MO (M ="
"red, blue, green, yellow, brown, black, or (uncommon) violet. There is a unique natural white spinel, now lost, that surfaced briefly in what is now Sri Lanka. Some spinels are among the most famous gemstones; among them are the Black Prince's Ruby and the ""Timur ruby"" in the British Crown Jewels, and the ""Côte de Bretagne"", formerly from the French Crown jewels. The Samarian Spinel is the largest known spinel in the world, weighing . The transparent red spinels were called spinel-rubies or balas rubies. In the past, before the arrival of modern science, spinels and rubies were equally known"
"Alunite Alunite is a hydrated aluminium potassium sulfate mineral, formula KAl(SO)(OH). It was first observed in the 15th century at Tolfa, near Rome, where it is mined for the manufacture of alum. First called ""aluminilite"" by J.C. Delamétherie in 1797, this name was contracted by François Beudant three decades later to alunite. Alunite crystals morphologically are rhombohedra with interfacial angles of 90° 50', causing them to resemble cubes. Crystal symmetry is trigonal. Minute glistening crystals have also been found loose in cavities in altered rhyolite. Alunite varies in color from white to yellow gray. The hardness is 4 and the"
"Dimorphite Dimorphite, chemical name tetraarsenic trisulfide (AsS), is a very rare orange-yellow arsenic sulfide mineral. In nature, dimorphite forms primarily by deposition in volcanic fumaroles at temperatures of 70–80 °C (158–176 °F). Dimorphite was first discovered in such a fumarole near Naples, Italy in 1849 by the mineralologist Arcangelo Scacchi (1810–1893). Since its discovery, dimorphite has been found in the Alacrán silver mine near Copiapó, Chile. It has also been reported from Cerro de Pasco, Peru, and the Lavrion District Mines in Attica, Greece. Dimorphite has two crystal forms, Α- and Β-. This property gives rise to its name, which"
"Aluminium oxynitride Aluminium oxynitride or ALON is a ceramic composed of aluminium, oxygen and nitrogen. It is marketed under the name ALON by Surmet Corporation. ALON is optically transparent (≥80%) in the near-ultraviolet, visible and midwave-infrared regions of the electromagnetic spectrum. It is four times harder than fused silica glass, 85% as hard as sapphire, and nearly 15% harder than magnesium aluminate spinel. Since it has a cubic spinel structure, it can be fabricated to transparent windows, plates, domes, rods, tubes and other forms using conventional ceramic powder processing techniques. ALON is the hardest polycrystalline transparent ceramic available commercially. Its"