opal

An opal is a gem, a semi-precious stone that comes in many shimmery, partly translucent colors. If your birthday is in October, an opal is your birthstone.

An opal is a mineral made of silica, and it's found within the cracks and notches of many different kinds of rock. Most of the world's supply of opals comes from Australia. A polished opal that's been set in a ring or necklace is usually several shades or colors — most often blues and greens — with sparkles or shimmers decorating the stone. The word opal comes from the Latin opalus, and its ultimate root is probably the Sanskrit upala, "precious stone."

Definitions of opal
1

n a translucent mineral consisting of hydrated silica of variable color; some varieties are used as gemstones

Types:
black opal
a dark colored opal with internal reflections of green or red
fire opal, girasol
an opal with flaming orange and yellow and red colors
harlequin opal
a reddish opal with small patches of brilliant color
Type of:
mineral
solid homogeneous inorganic substances occurring in nature having a definite chemical composition
opaque gem
a gemstone that is opaque

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