Trapiche

Trapiche is a rare growth pattern in which six sectors radiate from a central core, separated by dark spokes, so the stone looks like a wheel seen from above. The word is Spanish for the cane-crushing mill whose spoked wheel it resembles. It is famous in Colombian emerald, above all from Muzo and Peñas Blancas, and turns up occasionally in ruby, notably from Mong Hsu in Burma, and in sapphire. It is structure, not optics. The pattern is fixed in the crystal, laid down as it grew, and it does not move when the stone moves; that is what separates a trapiche from a star, which slides across a cabochon as the light shifts. The spokes themselves are foreign material, in emerald usually albite and dark carbonaceous matter, trapped between the growth sectors.

Trapiche is judged on the sharpness and symmetry of the spokes and on the colour of the sectors between them. A crisp six-armed pattern in good green is the prize; a smeared, lopsided one with a grey body is a curiosity.

On a lab report

Laboratories identify the material as natural emerald, ruby or sapphire and note the pattern in the comments, typically as "trapiche" or "trapiche-type", the second when the pattern is imitated by another species such as tourmaline or quartz. The treatment line still applies. Trapiche emerald is usually oiled like any other, and the filler grade should be on the report; trapiche ruby is examined for heat like any other. Most trapiche is cut as a slice or a low cabochon to show the wheel, so expect small weights and expect the report measurements to describe a flat piece.

Ask for the report rather than the story: which laboratory, which species, what filler, and whether the piece has been cut across the pattern or is a whole crystal section.