Feldspar
Introduction
A group of aluminosilicate minerals containing calcium, sodimu or potassium. The major rock-forming minerals in the feldspar group include albite, anorthite, orthoclase and microcline. In petrology, the group is split into two major subgroups, alkali (feldspar minerals poor in calcium, and mostly rich in potassium) and plagioclase (the albite to anorthite series).
It is the most abundant mineral in the Earth's crust.
Feldspare samples from the day workshop.
Moonstone
Is the trade name for a sodium potassium aluminiun silicate white feldspar with a blue schiller.
The name reflects the visual phenomenon called adularescence, caused by light difracting through alternating layers of orthoclase and albite feldspar, resulting in a soft, blueish sheen. Cut gemstones often display a cat's eye effect. Hardness 6-6.5 Mohs'. Favourite version for lapidaries and jewellers is the rainbow variety - a translucent feldspar with iridescent rainbow colours.
Arab Roots of Gemolgy
Some elements from 'Arab roots of gemolgy: Ahmad ibn Yusuf Al Tifaschi's Best Thoughts on the Best of Stones' (c.1240) trans. Samar Najm Abul Huda. The Scarecrow Press, London, 1998.
Moonstone cat's eye
Started in its host rock to be corundum but external factors prevented it, according to an increase or decreas in the four elements. Found in the same location as corundum and diamond.
This is a strange stone, the overlapping colour is white withan astonishing radiance coupled with a delicate transparent clarity, but a blueish spot can be seen inside it, similar to a cat's eye catching the light in its moving pupil. The best quality is the stron, white , transparent one with a clear spot showing little movement but great brightness.
Well known by gem experts that it protects its wearer from evil eyes and evil spirits, whether known or hidden, human or occult. has the properties of the bahraman ruby in addition to two great benefits: safeguards the omeny of the wearer and protects from misfortu e, the second that if worn by a man who particiated in a war and was defeated, if this man lay amongst the killed, all his enemies who come near him see him as dead and covered in blood , this are repelled.
A jeweller who visited Inda said it was worshipped there as idols are worshipped, it was more valuable there than in Arab lands. The value depends on demand for it and on people's knowledge of it properties.
