Ruby in Fuchsite matrix
Corundum is one of the most known gem varieties, as Ruby and Sapphire.
Ruby and Sapphire are scientifically the same mineral but differ in color.
Corundum is very hard and stable mineral, making it the second hardest mineral after Diamond.
It is unaffected by acids and most environments.
Translucent brown Corundum and Emery are the most common form of Corundum.
Corundum is easily synthesized.
Natural ruby and sapphire gemstones may have their color artificially enhanced or deepened through heat treatment.
Ruby is a variety of Corundum that takes it's red color from chromium impurities.
Saphire takes it's color from iron or titanium impurities.
Characteristics:
Formula: Al2O3
52,93% Aluminum; 47,07% Oxygen
Composition Aluminum oxide
Color: blue, red, violet, pink, green, yellow, orange, gray, white, colorless, black, multicolor
Streak white
Hardness 9 Mohs
Crystal system hexagonal
Forms hexagonally shaped prismatic and tabular crystals as bipyramidal hexagons; crystals are usually elongated and striated crosswise; crystals are commonly smooth or rounded on the edges due to alluvial action; crystals are sometimes striated or etched
Transparent to opaque
Specific gravity 3,9-4,1
Luster vitreous to adamantine
Cleavage none
Fracture uneven
Tenacity brittle
Rock type igneous, sedimentary, metamorphic
Special characteristics:
May fluorescence orange, yellow or red in shortwave UV; may triboluminescence
Insolubile in acids
High specific gravity, high hardness, distinctive crystal shape
Fluorescence activator: main Cr;
Peak: Cr replacing Al with peak at 693 and 694 nm
Ruby under Ultraviolet light
Tests:
May fluorescence orange, yellow or red in shortwave UV; may triboluminescence
Ruby has red fluorescence with strong intensity in long wave and medium intensity in mid and short wave
Sapphire may have red, orange or yellow fluorescence
Insolubile in acids
High specific gravity, high hardness, distinctive crystal shape
Varieties:
Emery - black, massive variety of Corundum with color caused by mixture of magnetite, hematite and spinel
Padparadschah - orange-pink variety of sapphire, very rare
Ruby - pink to red variety of corundum; color usually caused by inclusions of the metal chromium and can present asterism by having tiny inclusions parallel rutile needles in ruby; the chromium impurities can cause also the fluorescence which can be helpfull in its indentificaiton but not all rubies has fluorescence; most often it have; ruby is also pleochroic, displaying a lighter and more intense color when viwed at different angles
Burma Ruby - ruby from Burma, synonym of Burmese Ruby
Burmese Ruby - exceptional red ruby but not from Burma, occasionally also used to describe synthetic ruby
Pigeon's blood Ruby - highly desirable form of riby of a blood-red color with a hint of blue
Ruby Fuchsite - describes a dark red Ruby in green Fuchsite mica matrix found in India
Ruby Zoisite - Mixture of opaque red Ruby in green Zoisite from Tanzania, Ruby Zoisite has pretty contrast and is used as minor gemstone, being polished into cabochons and carved into ornamental figures
Sapphire - refers to all gem varieties of corundum, excluding red variety classified as ruby; on trade, usually refers to blue gem; the colors comes from impurities of iron or titanium
Star Ruby - ruby with asterism
Star sapphire - sapphire with asterism
Ultralite - incorrect term in the gem trade occasionally used to describe blue sapphire
Leucosapphire - colorless
Common mineral asociations: calcite, albite, muscovite, fuchsite, spinel, almandine, kyanite
Distinguishing similar minerals:
can be confused with many minerals but corundum has high hardness and specific gravity and easily distinguished
Ruby is identical to Ruby Spinel, and often occurs together in the same mineral environment
Garnet (particularly Pyrope) and red tourmaline (rubellite) may also resemble Ruby but Ruby is harder.
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