Tourmaline

Characteristics

• Crystal system (habit?) - hexagonal or trigonal
• Form - prismatic
• Hardness - 7-71/2 (tough)
• Cleavage - indistinct
• Fracture - uneven to conchoidal
• Streak - colourless
• Lustre - vitreous, resinous
• Colour - black, brown, green, pink

My sample of unknown origin, possibly Namibia?

Introduction

Is a group name that covers a number of species based on same basic chemical structure. Eleven minerals in the group. Inc. elbaite, schorl (black), dravite, liddicoacite, rubellite (red). Most tourmaline is dark and opaque but many transparent varieties are valued as gems, with the greatest range of any gem colours.

Most popular is electric blue to green Paraiba tourmaline, named for locality first found - north east Brazil in 1982. Colour comes from the presence of copper and manganese. Newer discoveries in Nigeria (2001) and Mozambique (c.2005) have produced spectacular stones, some over 60 carats.

Sources: Brazil for most; Burma, Sri-Lanka, Urals in Russia, Tanz., Mozam., Madag., Nigeria, Pakistan, Afghan., Maine USA, California USA.

Most deeply coloured ones show distinct pleochroism eg: red may show dep red and pink; greens show different shades. The green part has the most iron, and the pink colour is due to trace amounts of manganese.

Best crystals are found in pegmatites (coarse grained rocks related to granite) and metamorphosed limestone pockets in contact with granite magmas. Often found as crystals, some multicoloured with either at each end or forming colour zoned cores and rims. Cutting takes advantage of this to produce bi-coloured gems called 'parti-coloured' and 'watermelon'.

Used as gemstone, carvings and beads. If they have fluid filled growth tubes along the length of the crystal then may be cut to form cat's eye cabochons.

Treatments: Heat treated ones show neon glow and command high prices; results of various treatments are not always predictable; heat and irradiation used to improve colour; waxing & oiling used to mask fractures or fill cracks.

Not made as syn. gem so imitations only occur as other natural stones or glass.

Only recently noted it was used in past up to 2000 yrs ago. was not sufficiently distinct to be separated from similar stones like ruby or zircon. Dutch began to import it from East in 1700s. Name thought to derive from 'turamali' (Sinhalese meaning mixed precious stone or parcel of gem rough, which referred to yellow zircons from Ceylon/Sri l. From these mixed stones a new, lower density mineral was discovered. It attracted dust so was called 'ash drawer' or 'aschentrecker'. This led to further investigation and at beginning of 19th cent. tourmaline became a distinct mineral. Under temp. change was also seen to generate an electric charge and when this happens dust is attracted - so this gem needs more cleaning.

Blue Cap tourmaline

Elbaite tourmaline crystals showing a vivid blue termination on top of a contrasting body usually pink (traces of manganese), red or colourless.

Grow in lithium rich pegmatites. The chemistry changes during grow to create the blue top, iron becomes more dominant.

Found in California. Dec 1972 discovery by mine owners Ed Swoboda and Bill Larson (Tourmaline Queen Mine) is one of most significant finds in America for tourmalines. Specimens now in private collections. San Diego County, California, had a mining rush in late 1800s. Tiffany & Co. bought a lot and others went to China. Also found Brazil, Afghanistan and Namibia.

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.

Found where corundum is found, in the island behind the isalnd of Sarandeen in the mountain known as Djabal al Rahun. Also found near Bijadi, these stones being of better quality than the Indian ones.

Badjadi is a stone of wine colour, without brilliance, except for a few specimens which resemble ruby. If found in the host rock it is dark and opaque, only when cut by specialists does it colour and beauty appear and it becomes brillinat - best one is strong red with good brilliance. Does not shine unless foiled and underside is hollowed out.

Almandine garnet resembles tourmaline, dark in shade fo its underside need to be hollowed out. Less valuable than the tourmaline, and does not pick up any dust particles from the floor.

When tourmaline is rubbed against the hair or beard and placed on the floor, it picks up straw and other objects. If female animals - speaking or non-speaking - see this stone they become in heat and cannot control their senses. If worn in a ring (20 grains of barley worth) it prevents nightmares. Ibn Hamdan said it strengthened eyesight and remove veils and darkness.

Some gen dealers consider tourmaline as the last variety of garnet, in 5th palce after azbazashtti - it is priced at half of azbazashtti.