Emerald

Emerald is the green variety of beryl, a beryllium aluminum silicate, with its color produced by traces of chromium and sometimes vanadium. It is one of the four traditional precious gemstones alongside diamond, ruby and sapphire.

Emeralds are famous for their inclusions, lovingly called the "jardin" (French for garden). Unlike most gems, eye-visible inclusions are accepted and even expected in emerald, and they help confirm natural origin.

At hardness 7.5-8 emerald is fairly hard but brittle and often fractured, so it requires more careful handling than ruby or sapphire. Fine, richly saturated green stones, especially from Colombia, are extremely valuable.

Emerald forms where beryllium and chromium or vanadium meet, an unusual geochemical pairing because these elements normally occur in different rock types. This typically happens at boundaries between granitic/pegmatitic fluids and chromium-rich host rocks like schist or shale.

Colombia's world-famous deposits (Muzo, Chivor) are unusual hydrothermal vein systems in black shale and limestone, producing exceptionally fine color. Zambia, Brazil, Afghanistan and Russia (Ural Mountains) host schist-related emeralds.

The turbulent, fluid-rich growth conditions cause the characteristic fractures and inclusions found in most emeralds.

Look for a transparent to translucent green stone, often with visible inclusions and fractures, that has a hexagonal crystal habit and a vitreous luster. Emerald is hardness 7.5-8 and shows weak dichroism (green and bluish-green).

Natural emeralds typically display a "jardin" of internal inclusions; a completely clean, vividly green stone may be synthetic or a different material. Emerald has a relatively low refractive index for its brilliance, appearing soft and velvety rather than fiery.

Look-alikes include green tourmaline (verdelite), tsavorite garnet, peridot, green glass and green fluorite (much softer). Tourmaline shows stronger dichroism; tsavorite is singly refractive and brighter; glass shows bubbles and is softer.

Emerald is principally a gemstone, set in fine rings, necklaces and heirloom jewelry, and it is the May birthstone and a 20th- and 35th-anniversary gem. Historic emeralds adorn many crown jewels and museum collections.

Because emeralds are brittle and often fractured, most are treated with oils or resins to improve clarity; the type and extent of treatment significantly affects value. Stones should be protected from heat, ultrasonic cleaners and sharp blows.

Metaphysically, emerald is linked to love, renewal and the heart, though these associations are not scientific.