Tourmaline

Tourmaline is a group of minerals comprised of a complex boron-aluminum silicate with one or more of the following: magnesium, sodium, lithium, iron, potassium or other metals. It appears in light from dark red to purple as well as brownish variations of these hues - light to dark green, yellowish-green, greenish-yellow, brownish-orange. It also grows bi-coloured.

Varieties
Bi-coloured, watermelon, cat's eye, alexandrite-like (rare) .

Sources
Sri Lanka, Brazil, USA (California, Maine), Madagascar, Tanzania, Kenya, Russia, Afghanistan, Pakistan (prime new source).

History
Dutch children played with tourmaline because of its ability to attract light objects. The stones were called "aschentrekkers" (ash drawers).

Cuts & Uses
Any cut may be used. Some are carved, some fashioned into beads. Cat's eye are always cut en cabochon. Sometimes carved to make use of more than one colour.

Aquamarine

Aquamarine is a blue to greenish-blue or bluish-green variety of beryl.

Varieties
May occasionally exhibit a cat's eye effect (chatoyancy).

Sources
Sri Lanka, Brazil, Madagascar (only historically), Tanzania, Russia, Kenya, Afghanistan, Nigeria.

Toughness
Good

Treatments
Almost all aquamarine is heat-treated to enhance its blue colour. Irradiation with neutron, gamma rays or with x-rays. Colour change is permanent and is an accepted practice. A morganite (pink beryl) turns deep purple blue (Maxixe type) upon ultraviolet irradiation, though the colour is not stable.

History
The word aquamarine comes from the Latin for sea water. In 1910 a 243 lb. crystal was found in Brazil. The outside was greenish and the inside was blue. It sold for $25,000 and was cut into many high quality gems. The American Museum of Natural History has a 13 lb. uncut piece of the green outside portion.

Cuts & Uses
The step-cut is the most popular because it accentuates the colour. As it is often found in large, flawless, even-colored crystals, it is frequently used in pendants and rings. Given a piece of rough with a certain colour intensity, the larger stones cut from it will exhibit deeper colour.
Other Information Aquamarine is the blue, or perhaps more correctly, blue-green or aqua variety of the mineral beryl. Other gemstone colour varieties that belong to beryl include emerald, morganite, and heliodor. Other colours of beryl are simply referred to by their colour, such as red beryl. Most gem aquamarines have been heat treated to produce the popular blue-green varieties from less desirable yellow or pale stones.

cat's eye

Cat's eye

A cat's eye like effect, known as 'chatoyancy', appears to move on this stone's surface. Cat's eye is a gem variety of chrysoberyl.

Hardness: 8.5 on the Mohs' scale.

There are generally two varieties of cat’s eye – the alexandrite cat’s-eye and the chrysoberyl cat’s-eye, which is very popular in the Far East, particularly in Japan. The ideal colours of the chrysoberyl cat’s-eye are yellowish-brown, which is called the honey colour, and the yellow-green, which is called the apple green colour. A very good cat’s eye, apart from being of ideal colour, should have a high degree of transparency and a well-defined unbroken ray. It should be free from any distracting inclusions visible to the unaided eye. The chrysoberyl cat’s-eye is one of the most beautiful gemstones because of the “chatoyancy” or the eye effect.

Description
A translucent variety of chrysoberyl (beryllium aluminum oxide) which exhibits a silvery white line across the stone. This moves as the stone, the light source or the observer moves and may appear to open and close like an eye. The finest quality has a sharp eye that appears to open and close as the stone is rotated, and exhibits a strong "milk and honey" effect (stone on one side of the eye appears lighter than the other). These colours switch as the stone or light source is moved. The most highly prized body colours are greenish-yellow and brownish-yellow (honey colour).

Varieties
Rare specimens also exhibit change of colour.

Sources Sri Lanka, Brazil.

Phenomena
Chatoyancy caused by the reflection of light off minute, parallel, needle-like rutile crystals or hollow tubes.

Toughness
Excellent

Miscellaneous
When a gem specimen exhibits both chatoyancy and change of colour, one or both phenomena will suffer. It is more common to find a good eye with poor change of colour. The conditions necessary for one phenomenon conflict with those needed for the other. The term cat's eye when used alone refers to chrysoberyl. Other minerals exhibiting chatoyancy must be qualified, e.g. tourmaline cat's eye.

History
Cat's eye has been regarded as a preserver of good fortune. The natives of Sri Lanka still consider it a charm against evil spirits. British royalty often use it as an engagement stone.

Cuts & Uses
Must be cut in a cabochon to produce cat's eye effect. This should be cut so that the long portion of the cabochon is 90 degrees to the direction of the needles.