Topaz

Group: Silicate Colour colourless, yellow, brown-red, pale blue, pale red, red, purple, pale green Pleochroism: yellow: strong – lemon-yellow, honey, straw red: strong – dark red, pink, yellow blue: weak – pale blue, pink, colourless Mohs’ hardness: 8 Density: 3.49 - 3.60 Cleavage: perfect, parallel to the base of the crystal Fracture: conchoidal Crystal system: rhombic, prisms Transparency: transparent Lustre: vitreous lustre Fluorescence: very weak: pink -> brown Red -> yellow-brown Yellow -> orange-yellow

In ancient times the Topaz was believed to calm passions, protect fields from hail and even, if carried in the mouth, protect from the Black Death. Its name comes from one of the most ancient deposits: the island Zebirget, in the Red Sea, earlier called Topazos. The Topaz is an especially brilliant stone and the most sought for colours are yellow, orange (Imperial Topaz), blue and pink. In some rare cases, it can also be red or purple.

Only the corundum (ruby and sapphire -> 9 in the scale of Mohs) or the Diamond (10 in the scale of Mohs) are harder than the Topaz, which is heavy and relatively porous. It is also the only transparent mineral which has the same density as the Diamond. It is very resistant to acids and it is very difficult to melt. For some Topazes, heating up leads to loss of colour and in others, to the increasing of the colour’s depth: yellow Topazes turn reddish if heated up to 300-400C. Topazes are usually very pure, although they can have inclusions. The most valuable colour is rose.

It is usually found in cavities in granite and similar rocks. The most important deposits are in Brazil, Pakistan, the Urals, Mexico, Sri Lanka, Madagascar and Nigeria.

The most usual cut is a very faceted oval cut, although emerald and princess cut are also common. More rarely and only for stones of a lesser quality, they can be cut in a cabochon.

The yellow topaz is similar to the citrine, although the only thing both gemstones have in common is the colour. Experts differentiate the topaz by its strong lustre and Mohs’ hardness. Pale blue topazes are sometimes used instead of the much more valuable aquamarine. It can also be confused with a ruby, a sapphire or a tourmaline.