n. [ L. opalus: cf. Gr. &unr_;, 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 ]

☞ 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 ]

v. i. [ imp. & p. p. Opalesced p. pr. & vb. n. Opalescing ] To give forth a play of colors, like the opal. [ 1913 Webster ]

n. (Min.) A reflection of a milky or pearly light from the interior of a mineral, as in the moonstone; the state or quality of being opalescent. [ 1913 Webster ]

a. Reflecting a milky or pearly light from the interior; having an opaline play of colors. [ 1913 Webster ]

n. 1. An opaline variety of yellow chalcedony. [ Webster 1913 Suppl. ]

2. Opal glass. [ Webster 1913 Suppl. ]

3. An opaline color or expanse. [ Webster 1913 Suppl. ]

a. [ Cf. F. opalin. ] Of, pertaining to, or like, opal in appearance; having changeable colors like those of the opal. [ 1913 Webster ]

v. t. [ imp. & p. p. Opalized p. pr. & vb. n. Opalizing. ] [ Cf. F. opaliser. ] To convert into opal, or a substance like opal. Lyell. [ 1913 Webster ]

n. [ Opal + -type. ] (Photog.) A picture taken on “milky” glass. [ 1913 Webster ]