Any naturally occurring mineral substance which is clear and transparent like ice; esp. a form of quartz (= rock crystal, n. 1). Often in…

A hexagonal prismatic crystal (mentioned by Pliny Nat. Hist. xxxvii. ix. 52).

Originally and chiefly Scottish. Crystal, as a precious material. Cf. crystal, n. 2a. Obsolete.

= rainbow crystal n.

a variety of quartz found in Cornwall; a crystal of this quartz.

transferred. Applied (usually with distinguishing epithet) to other crystalline minerals, resembling the diamond in brilliancy; as Bristol diamond…

quartz; a quartz crystal.

Quartz in the form of transparent colourless crystals (usually hexagonal prisms).

A variety of colourless transparent rock crystal (quartz), formerly used instead of glass in spectacles; a lens made of this. Cf. compounds 1b. Obs…

†(a) = Cornish diamond n.; (b) Cornish granite in a state of partial decomposition, ground and used with clay in the manufacture of earthenware.

= rock crystal, n.

an iridescent variety of rock crystal.

Quartz in crystalline form, rock crystal; a piece or single crystal of this, (later esp.) one used in a clock or other device.

(a piece of) rock crystal (from Ireland); (formerly also) †marcasite (obsolete).