Topaz

Topaz is an aluminum fluorosilicate gemstone famous for its hardness of 8 on the Mohs scale and its glassy brilliance. It occurs in a wide range of colors: colorless, blue, yellow, golden, the prized pink-orange 'imperial' topaz, brown, and pink.

It crystallizes in the orthorhombic system, often as well-formed prismatic crystals with characteristic lengthwise striations, and it has perfect basal cleavage that cutters must respect.

Much of the bright blue topaz on the market is colorless topaz that has been irradiated and heated. Topaz is the traditional birthstone for November (golden) and, with blue topaz, December.

Topaz forms in fluorine-rich igneous environments, especially in cavities and miarolitic pockets of granites and granitic pegmatites, and in rhyolite lava flows. It also occurs in high-temperature hydrothermal veins and greisens.

Fluorine-bearing vapors and fluids late in the crystallization of granitic magma carry the elements that build topaz crystals in open cavities, where they can grow large and clean.

Famous sources include Brazil (Minas Gerais, the main source of imperial topaz), Pakistan, Russia's Ural Mountains, Nigeria, Sri Lanka, Mexico, and Utah's topaz-bearing rhyolites in the USA.

Topaz is identified by its high hardness (8), strong vitreous luster, good transparency, and relatively high density (it feels heavy for its size). Crystals are prismatic with lengthwise striations and show one direction of perfect cleavage. Streak is white.

It often shows pleochroism, and pink-orange imperial stones are especially distinctive.

Look-alikes: Quartz (citrine, smoky) is softer (7) and lacks topaz's perfect cleavage and higher density. Aquamarine is a beryl, also hard, but topaz is denser. Much 'blue topaz' is treated colorless topaz. The hardness, heft, and basal cleavage help separate topaz from quartz and beryl.

Topaz is principally a gemstone, cut into a vast range of jewelry. Colorless topaz is irradiated and heated to produce the popular blue shades (sky, Swiss, and London blue), while natural imperial and pink topaz are rare and valuable.

Its hardness makes it durable for rings and pendants, though the perfect cleavage means it can chip if struck sharply. Large flawless crystals are also collected as specimens.

As a November and December birthstone, topaz symbolizes strength, clarity, and good fortune. In metaphysical use golden topaz is linked to confidence and abundance, and blue topaz to communication.