crystal

crystal originally, ice, or a clear and transparent mineral resembling ice; a form of quartz (especially rock-crystal) having these qualities, which in ancient and medieval belief was thought to be congealed water or ice which had been ‘petrified’ by some natural process. Crystal was believed to have magic powers, and is taken as the type of something characterized by purity and clarity. The word is recorded from late Old English, and comes via French and Latin from Greek krustallos ‘ice, crystal’.

From the early 17th century, crystal developed the sense in chemistry of a piece of a homogeneous solid substance having a natural geometrically regular form with symmetrically arranged plane faces.
crystal-gazing looking intently into a crystal ball with the aim of seeing images relating to future or distant events.
crystal healing the use of the supposed healing powers of crystals in alternative medicine.
Crystal Palace a large building of prefabricated iron and glass resembling a giant greenhouse, designed by Joseph Paxton for the Great Exhibition of 1851 in Hyde Park, London, and re-erected at Sydenham near Croydon; it was accidentally burnt down in 1936.
crystal wedding in the US, a 15th wedding anniversary.