Lexitechnia

Pliny the Elder, Naturalis Historia 37.10, on quartz crystals:

Quæ vero sine vitio sint, pura esse malunt, acenteta appellantes, nec spumei coloris, sed limpidæ aquæ.

Those which are in fact flawless are preferred uncut and are called acenteta; and they are not cloudy in color, but of the color of clear water.

Acentetum is from the Greek άκέντητος, meaning ‘unpricked’ or possibly ‘unembroidered’.  Lewis and Short give the Latin meaning as ‘without points or spots’, presumably in reference to the clarity of the crystal, but it might just as well be ‘without engraving’; as Pliny states, quartz was usually decorated by engraving to hide or deemphasize the imperfections in the crystal, but acenteta didn’t get this treatment, but were preferred pura.