Friday, May 29, 2009
Bloodstone
Bloodstone is a variety of chalcedony which is cryptocrystalline quartz. It is green plasma containing red spots of jasper, which look like spots of blood giving the stone its descriptive name. The green colour is due to the presence of masses of chlorite, and the red spots are inclusions of red coloured jasper. It is usually cut en cabochon, or into beads, but most often used as a sealstone, and is popular in gents' signet rings. It is often quite coarse and therefore is closely related to jasper, another group of quartz.
It is also called heliotrope although this name is hardly ever used nowadays.
The name bloodstone is sometimes misleadingly used for haematite.
It is also called heliotrope although this name is hardly ever used nowadays.
The name bloodstone is sometimes misleadingly used for haematite.
Sources
The best bloodstone is obtained from India, other sources include USA, Brazil, and Australia.
The best bloodstone is obtained from India, other sources include USA, Brazil, and Australia.
Tuesday, May 19, 2009
Beryl
Varieties
Beryl exists in a number of different varieties, some being better known by their own name, for example, emerald is the grass green variety and aquamarine is the sky blue variety.
Colouration
Pure beryl is colourless, often called white, and although quite rare, tends not to be valuable because it does not have much brilliance. Colours, as in many gemstones, are caused by small amounts of impurity, usually metallic oxides. This is another case where impurity is desirable.Chromium, in the form of chromic oxide, causes the bright grassy green colouring in beryl, thereby producing beryls.Vanadium can also affect the exact shade, as may traces of iron.It is also possible to have green beryl which is not emerald, because the colouring agent is not chromium.
Hardness
Beryl is quite hard, having a hardness of 71/2 to 8 on Moh's scale, compared with 10 for diamond, 9 for corundum, and 8 for topaz. Hardness is generally a desirable feature is gemstones.
Cleaning
Beryl jewellery can be carefully cleaned using warm soapy water, or detergent, rinse thoroughly afterwards as detergents can cause dermatitis and allergic reactions. Enzyme cleaners should be avoided for the same reasons. Brushing with an old tooth brush to remove dirt and grease will also help. Cleaning agents containing chlorine may have a detrimental effect on low carat gold alloys, so are best avoided.We stress that reasonable care should be taken when cleaning emeralds, as washing with strong detergents could cause any oil to be diluted or removed, requiring the stone to be re-oiled.Beryls do not like excessive heat, and although they can tolerate temperatures above 100c (the boiling point of water), it is advisable to use warm water rather than hot water, to reduce the dangers of thermal shock.It is not advisable to clean beryl in an ultrasonic tank. We sometimes risk it with our own stock, but we would never clean a large or valuable beryl which did not belong to us, in an ultrasonic machine.
Beryl exists in a number of different varieties, some being better known by their own name, for example, emerald is the grass green variety and aquamarine is the sky blue variety.
Colouration
Pure beryl is colourless, often called white, and although quite rare, tends not to be valuable because it does not have much brilliance. Colours, as in many gemstones, are caused by small amounts of impurity, usually metallic oxides. This is another case where impurity is desirable.Chromium, in the form of chromic oxide, causes the bright grassy green colouring in beryl, thereby producing beryls.Vanadium can also affect the exact shade, as may traces of iron.It is also possible to have green beryl which is not emerald, because the colouring agent is not chromium.
Hardness
Beryl is quite hard, having a hardness of 71/2 to 8 on Moh's scale, compared with 10 for diamond, 9 for corundum, and 8 for topaz. Hardness is generally a desirable feature is gemstones.
Cleaning
Beryl jewellery can be carefully cleaned using warm soapy water, or detergent, rinse thoroughly afterwards as detergents can cause dermatitis and allergic reactions. Enzyme cleaners should be avoided for the same reasons. Brushing with an old tooth brush to remove dirt and grease will also help. Cleaning agents containing chlorine may have a detrimental effect on low carat gold alloys, so are best avoided.We stress that reasonable care should be taken when cleaning emeralds, as washing with strong detergents could cause any oil to be diluted or removed, requiring the stone to be re-oiled.Beryls do not like excessive heat, and although they can tolerate temperatures above 100c (the boiling point of water), it is advisable to use warm water rather than hot water, to reduce the dangers of thermal shock.It is not advisable to clean beryl in an ultrasonic tank. We sometimes risk it with our own stock, but we would never clean a large or valuable beryl which did not belong to us, in an ultrasonic machine.
Aquamarine
Varieties
Aquamarine is the sky blue or sea blue variety of beryl, sometimes it is sea green, and less desirable.The word aquamarine literally means seawater, and is very frequently shortened to aqua.
ColourationThe colour of aquamarine is due to the presence of traces of iron present as an impurity in the crystal structure of beryl.
Heat Treatment
As with many gemstones, the colour of aquamarine has almost always been improved by treatment of some kind. Heat treatment is used for aquamarines, to turn greenish, yellow or brown stones into a beautiful blue. The stones are heated to about 400 to 450 degrees Celsius, and the colour change is permanent.
Colour Saturation & Size
Even the best aquamarines are fairly pale compared with other gemstones such as sapphire. Large stones benefit from the effects of colour saturation, and as aquamarine, unlike emerald, tends to form quite large clear crystals, this means that large aquamarines are relatively easy to find, and the price does not rise so steeply with size as it does with many other stones.It also means that small stones often lack colour intensity and are therefore not as attractive. Small aquamarines with good colour are therefore harder to obtain, and relatively expensive for their appearance. For small stones it may be preferable to use Ceylon sapphire instead.
Hardness
Aquamarine is quite hard, having a hardness of 71/2 to 8 on Moh's scale, compared with 10 for diamond, 9 for corundum, and 8 for topaz. Hardness is generally a desirable feature is gemstones.
Prices
The price range of aquamarine is very large, ranging from a few pounds per carat.
Cleaning
Aquamarine jewellery can be carefully cleaned using warm soapy water, or detergent, rinse thoroughly afterwards as detergents can cause dermatitis and allergic reactions. Enzyme cleaners should be avoided for the same reasons. Brushing with an old tooth brush to remove dirt and grease will also help. Cleaning agents containing chlorine may have a detrimental effect on low carat gold alloys, so are best avoided.We stress that reasonable care should be taken when cleaning emeralds, as washing with strong detergents could cause any oil to be diluted or removed, requiring the stone to be re-oiled.Aquamarines do not like excessive heat, and although they can tolerate temperatures above 100c (the boiling point of water), it is advisable to use warm water rather than hot water, to reduce the dangers of thermal shock.It is not advisable to clean aquamarine in an ultrasonic tank. We sometimes risk it with our own stock, but we would never clean a large or valuable aquamarine which did not belong to us, in an ultrasonic machine.
Apatite
Apatite
Apatite is a common mineral with a wide and attractive range of colours. In non-gem quality, very large crystals occur weighing up to several hundredweight. Clear gem quality crystals, though, are quite scarce and always small. It is too soft to be commonly used in jewellery, particularly in rings. It sometimes occurs with chatoyancy (cat's eye effect).
Colour
Colourless (white), pink, yellow, green, blue, and violet.
Apatite is a common mineral with a wide and attractive range of colours. In non-gem quality, very large crystals occur weighing up to several hundredweight. Clear gem quality crystals, though, are quite scarce and always small. It is too soft to be commonly used in jewellery, particularly in rings. It sometimes occurs with chatoyancy (cat's eye effect).
Colour
Colourless (white), pink, yellow, green, blue, and violet.
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