Topaz

Specific Gravity: 3.54
Refractive Index: 1.62-1.63
Birefringence (DR): 0.010
Luster: Vitreous
Crystal Structure: Orthorhombic
Composition: Aluminum fluorohyroxysilicate
Hardness: 8

Topaz occurs in a range of different colors. Deep golden yellow topaz (sometimes called sherry topaz) and pink topaz are the most valuable. Natural pink topaz is rare – most pink topaz is heat-treated yellow stone. Much colorless topaz is irradiated and heat-treated to a range of blues, some almost indistinguishable from aquamarine when seen with the naked eye.

Some topaz has tear-shaped or several immiscible (non-mixing) liquids. Other inclusions such as cracks, streaks, and veils also occur. Prismatic topaz crystals have a characteristic lozenge-shaped cross-section and striations parallel to their length. Topaz has one perfect cleavage.

When set in gold and worn around the neck, topaz is reputed to dispel bad omens, heal poor vision, and calm anger. A rough topaz crystal has characteristic wedge-shaped ends. Some crystals may show tear-shaped inclusions. It is common to find a topaz crystal in pegmatite rock.

Blue topaz may be produced by heat-treating colorless topaz. The stone is usually partially cut before treatment. Blue topaz is a popular variety of gemstones.

In the 17^th century, the Braganza diamond (1,640 carats) in the Portuguese crown was thought to be the largest diamond ever found. This was never confirmed and it is now believed to have been a colorless topaz. The name topaz is thought to be derived from the Sanskrit word tapas, meaning fire.

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Occurrence

Topaz occurs in igneous rocks such as pegmatites, granites, and volcanic lavas. It may also be found in alluvial deposits as waterworn pebbles. Localities include Pakistan, Mexico, Brazil, the USA, Sri Lanka, Japan, Africa, Australia, Tasmania, Myanmar (Burma), and the former USSR. Pakistan, Russia, and Brazil are the sources of pink topaz.