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CARNELIAN
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A member of the oxide group with the chemical formula SiO2. It has a red/orange colour and is one of my favourite gemstones. It has the same chemical composition as chalcedony and is a coloured form of quartz. It is 7 on the mohs scale (this measures hardness with 10 being the highest). It's orange colouring is due to the presence of iron impurities.
It is found in rock cavities, particularly in volcanic lava and tends to develop from silica rich solutions. Some of the oldest deposits can be found in India.
Related Gemstones:-chalcedony, sard
A member of the carbonate group with the chemical formula MnCo3. It is softer on the mohs scale than carnelian (3.5-4.5) and is pink. It is an important ore of manganese and it is this which gives it it's pink colour.
It may be found in veins of copper and lead in a variety of locations.
It's name is derived from the Greek word rhodus which means rose.
It often has alternating bands of dark and light pink and in my opinion is one of the prettiest gemstones. Although the finest rhodochrosite is pink, in some deposits manganese is partly substituted by calcium. This gives it an orange appearance.
