THOMSONITE
Specimen thm-4

Dims: 1.3 x 1.1 x 0.4" (3.2 x 2.7 x 1.1 cm)

Wt: 11 g

Minnesota, U.S.A.

This polished thumbnail specimen consists of a polished piece of a black (probably basalt) matrix that contains several Thomsonite "eyes". Each "eye" consists of an acicular spray of Thomsonite needles that extends from a more massive, concentrically-layered base. None of the Thomsonite crystals are isolated and free of the black matrix, and all that are visible are incomplete due to the grinding and polishing process. They have a milky-white coloration, but some have a pale pink tinge. Their round, layered bases have a color that ranges from pale pink to a brownish-red, and polish to a high gloss. A small chunk has been broken out of one of the rounded edges.

Dims: 1.6 x 1.6 x 1.2" (4.2 x 4.1 x 3.0 cm)

Wt: 1.4 oz. (41 g)

Minnesota, U.S.A.

This small hand specimen consists of a vein of massive, acicular and fibrous, radiating Thomsonite that extends between two thin basalt slabs. The crystals do not exceed 0.2" (5 mm) in length, and though many of the exposed needles are damaged and all appear to be somewhat weathered, their orthorhombic form is likely definable. The crystals have a dull white coloration and only a dull pearly or greasy luster at best. The compact, more massive Thomsonite beneath them has a color that ranges from white to pale brown and a dull, almost silky luster.

Dims: 1.97x1.46x0.79" (5.0x3.7x2.0cm)

Wt: 1.07oz. (30.3g)

Globe, Oregon, USA

A half-dozen globes of white thomsonite lie on a crust of heulandite in this specimen. The thomsonite balls have a distinct texture, looking very much like tiny snowballs (although having a slightly off-white color). The heulandite crystals are transparent and colorless. Tiny amounts of another mineral disturb the perfection of the thomsonite balls by giving an appearance of dirt on the surface, in several small areas. Still, this is an unusually nice specimen of this rare mineral.

Dims: 1.38x0.98x0.51" (3.5x2.5x1.3cm)

Wt: 0.24oz (6.8g)

Cape Grim, Tasmania, Australia

This specimen is all thomsonite, as one (and a fraction) globes of acicular crystals. Close examination reveals that the individual crystals are colorless, transparent, square in cross section, and some have basal terminations (unlike the similar mineral natrolite).