Geological of Corundum Family
- Family includes: Sapphire, Ruby
- Ruby has fluorescence! Sapphire can show star patterns!
General Identification
- Type: Mineral
- Class: Oxides
- Member of Group: Hematite
- Mohs Hardness: 9
- Formula: Aluminium oxide, Al2O3
- Crystal System: Trigonal
- Crystal Habit: Steep bipyramidal, tabular, prismatic, rhombohedral crystals, massive or granular
- Lustre / Diaphaneity: Adamantine to vitreous, Transparent, translucent to opaque
- Colour: Colorless, gray, brown; pink to red, orange, yellow, green, blue, violet; may be color zoned, asteriated mainly grey and brown
Ruby
- Gem stone, the red colour is caused mainly by the presence of the element chromium.
- Ruby fluoresces with UV light. Regular corundum does not.
- Has a variety which shows a three-point or six-point asterism or "star" under certain light conditions amd known as "Star Ruby".
- Red corundum is often sold as ruby.
- It may even be coloured and is often brown corundum.
- Red spinels, red garnets, and colored glass have been falsely claimed to be rubies.
- Quality is improved through heating, improving transparency by dissolving rutile inclusions, healing of fractures (cracks) or even completely filling them.
- More geological information.
- Colours: Red. Pink colour is debated as to whether it will be classified as ruby or sapphire.
Sapphire
- Colour determined by trace amounts of elements such as iron, titanium, chromium, copper, or magnesium.
- Mainly used for jewellery, abrasives, infrared optical components, high-durability windows, wrist-watch crystals and movement bearings, and very thin electronic wafers for very special-purpose solid-state electronics.
- Has a variety which shows a "star" under certain light conditions amd known as "Star Sapphire".
- A rare variety is known as color-change sapphire, exhibits different colors in different light.
- 95% of all the world's sapphires were being heated to enhance their natural color.
- Can be confused with Iolite which is called "Water Sapphire" to add to confusion. But iolite shows as a grey tone when looked from the side.
- More geological information.
- Colours: Any color except red. Best known for blue.
Emery
- Black granular corundum intimately mixed with magnetite, hematite, or hercynite
Geuda
-
Form of the mineral corundum, or sapphire, found primarily in Sri Lanka. Around 70%-80% of gems mined in Sri Lanka belong to geuda varieties.
-
Semitransparent and milky appearance due to rutile inclusions, these stones have little value as gemstones in their natural state.
-
Once heated they rival other natural sapphires for look.
Special Notes
- It is commonly used as an abrasive on everything from sandpaper to large tools.
- High quality versions are part of the precious gem category. Cost of natural crystals varies depending on their colour, clarity, size, cut, quality and geographic origin.
- Nowadays most sapphires and rubies now sold in jewellery stores are synthetic
- same composition but lacking healing qualities of natural grown pieces.
- jewelers prefer synthetic as colour is consistent and cutting and setting has little to no risk of damage as there are no imperfections.
- "Ruby in XXX" where xxx is fuchsite, kyanite and/or zoisite is with real ruby.
- All components are visible but which name used depends on what the mines or wholesalers felt was the more sellable name.