Judging quality
Look for translucent wedge-shaped crystals with glassy faces and clean edges. French Alpine material from the Oisans is the historical benchmark.
Silicate
Sharp axe-blade crystals in clove brown with violet flashes, strongly pleochroic and unmistakable once seen.

Look for translucent wedge-shaped crystals with glassy faces and clean edges. French Alpine material from the Oisans is the historical benchmark.
Brittle at the thin edges. Handle by the body of the crystal.
The classic Alpine locality of Bourg d'Oisans has been collected since the eighteenth century and defined the species.
Cultural history, recorded as tradition rather than as medical or scientific claim.
See it in person
Both rooms are open six days a week, and there is always someone happy to pull pieces out of the case so you can compare them under the light.