from
The Collaborative International Dictionary of English v.0.48
Opal \O"pal\, n. [L. opalus: cf. Gr. ?, Skr. upala a rock,
stone, precious stone: cf. F. opale.] (Min.)
A mineral consisting, like quartz, of silica, but inferior to
quartz in hardness and specific gravity.
[1913 Webster]
Note: The {precious opal} presents a peculiar play of colors
of delicate tints, and is highly esteemed as a gem. One
kind, with a varied play of color in a reddish ground,
is called the {harlequin opal}. The {fire opal} has
colors like the red and yellow of flame. {Common opal}
has a milky appearance. {Menilite} is a brown impure
variety, occurring in concretions at Menilmontant, near
Paris. Other varieties are {cacholong}, {girasol},
{hyalite}, and {geyserite}.
[1913 Webster]