It's softer than quartz (4 letters)

{ Answer }

OPAL

{ Related Clues }

Gem
Gemstone
Girasol
___ glass
Hyalite
Brooch stone
Cacholong or hyalite
Fiery gemstone
Form of silica
Iridescent gem
Iridescent mineral
J.E.C.'s birthstone
Oct. birthstone
An October birthstone
October birthstone
October gem
October stone
Oct.'s birthstone
Oct.'s gem
Oculus mundi
Ring setting
Semiprecious stone
Shade of gray
Solitaire item
Whitish gem
Birthstone after sapphire
Destructive 1995 hurricane
Gem with a play of colors
Memorable 1995 hurricane
Stone for Jimmy Carter
Stone for a Libra, traditionally
Stone of many colors
Stone of many Libras
Translucent precious stone
Word with black or fire
Stone made of silicon and oxygen
Word after fire or harlequin
It's less dense than quartz

{ Tags }

birthstone, cacholong, eg, fire, gem, gemstone, girasol, hyalite, iridescent, its, libras, many, milky, mundi, october, oculus, opal, shade, silica, stone, white

{ Notes }

The answer OPAL is very common and appears about once every 41.0 puzzles.

{ Definition }

OPAL as a noun:

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