Gemstones – a guide
Agate is a banded form of finely-grained, microcrystalline quartz. The lovely colour patterns and banding make this translucent gemstone very unique. Agates can have many distinctive styles and patterns, but each agate is unique.
Amethyst is one of the most popular gemstones, and has been considered valuable since ancient times. Its name derives from the Greek “amethystos”, which means “not drunken”, as Amethyst in antiquity was thought to ward off drunkenness. Amethyst colors range from light to dark purple, and the transparent deep purple colours are the most highly regarded.
Aquamarine, named for the Latin phrase “water of the sea”, is the blue to blue-green variety beryl. Beryl also contains other gem varieties, including emerald, and some lesser known varieties such as morganite and heliodor. Aquamarine ranges in colour from a faint light blue to blue and bluish-green, with lighter coloured stones being the more common type.
Aventurine is a compact variety of quartz/chalcedony containing small included flakes or scales that give it a glistening effect. Though the colour of Aventurine is most often associated with green, it can also be other colours such as gray, orange, and brown. However, colour types other than green are uncommon, and rarely used as gemstones or ornamental material.
Carnelian is the red, orange, or amber variety of chalcedony. Though often a solid colour, it may also be banded, in which case it would be jointly classified as both agate and Carnelian. Carnelian is an ancient gemstone, having been used as gem material since antiquity. Although still classed as a gemstone today, its significance and value has been diminished since the ancient times.
Cat’s Eye describes a gemstone polished into a cabochon that displays a narrow band of concentrated light going across the width of the stone. This effect, known as chatoyancy, or cat’s eye effect, is caused by inclusions of fine, slender parallel mineral fibres in the gemstone that reflect light in a single band.
Citrine is the yellow to orange variety of quartz. Natural Citrine is not common; most citrine on the gem market is produced by heat treating amethyst and smoky quartz. It takes a relatively low temperature to change the colour light to golden yellow, and heating to higher temperatures will give the stone a darker yellow to brownish-red colour. The name citrine is derived from the citron fruit, a yellow fruit similar to the lemon. (In fact, citron means “lemon” in several languages.)
Diamond, the most famed and fabled of all gemstones, is very unique in many ways. Renowned for being the hardest substance on earth, its sparkling fire, durability, and rarity make Diamond the most prized of all gems. No gemstone contains as much allure and interest as a diamond.
Emerald, the green variety of beryl, is the most famous and valuable green gemstone. Its beautiful green colour, combined with durability and rarity, make it one of the most expensive gemstones. Deep green is the most desired colour in Emeralds. In general the paler the colour of an Emerald, the lesser its value.
Garnet is not a single mineral, but describes a group of several closely related minerals. Garnets come in a variety of colours and have many different varieties. However, the most widely-known colour of garnet gemstones is dark red. When the term “garnet” is used, it usually refers to the dark red form.
Lapis Lazuli is a deep blue opaque gemstone, used in antiquity and continuously used throughout the generations. It still continues to be popular today, and remains one of the most important opaque gemstones.
Moonstone is the most well-known gemstone of the feldspar group. Named for its glowing colour sheen that resembles the moonlight, this phenomenon is caused by structural anomalies within the crystal formation.
Opal is the most colourful of gems. Its splendid play of colour is unsurpassed, and fine examples can even be more valuable than diamond. The play of colour consists of iridescent colour flashes that change with the angle at which the stone is viewed. This phenomenon is often called opalescence. The intensity and distribution of the colour flashes is a determining factor in the value of an Opal.
Pearls have been highly valued as gemstones since antiquity, and their allure and beauty has always been magnified by the difficulty of obtaining them in early times. Unlike most other gemstones which are minerals, pearls are organic and are formed by living organisms. They are generally formed within the soft tissue layer of molluscs such as oysters and mussels.
Quartz is one of the most common and varied minerals on earth, and its abundant colours produce many gemstone types. Amethyst and citrine are the most popular and valuable gem varieties of quartz, but other forms also make important gemstones.
Rose Quartz is the rosy pink variety of quartz. Its colour is usually soft, ranging from very light pink to medium pink in intensity. It is often hazy or turbid, which makes it lack good transparency. Rose Quartz is fairly common and found in many places throughout the world, and can occur in very large examples in nature. This allows exceedingly large gemstones to be cut from it. The relative abundance of Rose Quartz, and its frequent lack of full transparency, diminish its importance as a pink gemstone in relation to other pink gemstones such as topaz, tourmaline and kunzite.
Ruby is distinguished for its bright red colour, being the most famed and fabled red gemstone. As well as its bright colour, it is a most desirable gem due to its hardness, durability, lustre, and rarity. Transparent rubies of large sizes are even rarer than diamonds. Ruby is the red variety of the mineral corundum. Sapphire, the other gem variety of corundum, encompasses all colors of corundum aside from red. In essence, ruby is a red sapphire, since ruby and sapphire are identical in all properties except for colour. However, because of the special allure and historical significance, ruby has always been classified as an individual gemstone, and is never identified as a form of sapphire.
Sapphire is the most precious and valuable blue gemstone. It is a very desirable gemstone due to its excellent colour, hardness, durability, and lustre. In the gem trade, sapphire without any colour prefix refers to the blue variety of the mineral corundum.
Smoky Quartz is the brown “smoky” variety of quartz. It ranges in colour from light grayish-brown to deep black. Smoky Quartz can be opaque, but is almost always transparent to translucent, even when in its darkest colour shade. Smoky Quartz is very common and was never an historically important gemstone. Only in very recent times has it become a popular gemstone.
Topaz makes an ideal gem. A good hardness and desirable colours, combined with a relative abundance and availability makes it one the most popular gemstones. The most valuable colours of Topaz are the golden orange-yellow type, called Imperial Topaz and the dark pinkish-red and orange-red colours. Value increases with a deepness of colour in orange and reddish hues. The most commonly used colours of Topaz in jewellery are the blue types. It was not until this past century that blue Topaz became widespread on the gem market, since virtually all blue gem Topaz is irradiated and heat treated.
Tourmaline is the most colourful of all gemstones. It occurs in all colours, but pink, red, green, blue and multicoloured are its most well-known gem colours. Scientifically, tourmaline is not a single mineral, but a group of minerals related in their physical and chemical properties. The mineral elbaite is the member of the Tourmaline group that is responsible for almost all the gem varieties.
Turquoise is an ancient gemstone, and has been highly regarded in many of the world’s civilizations. Among the ancient empires it is best known among the Persian and Native American civilizations, where it was the most popular ornamental gemstone. Turquoise today remains a popular gemstone, and is one of the most important opaque gemstones. It is highly regarded due to its unique turquoise-blue colour, and is the only gemstone to have an exclusive colour named after it.
With thanks to – Minerals.net/gemstones