Quartz
The reference stone of the mineral world. Clear quartz grows as six-sided prisms terminated by a point, and its combination of hardness, transparency and abundance has made it the most collected crystal on earth. Quality runs from cloudy commercial material to water-clear Himalayan and Brazilian points with mirror-bright faces.
Look for glassy lustre on the natural faces, sharp undamaged terminations, and internal clarity that is either genuinely water-clear or interestingly veiled with phantoms, rainbows or inclusions. Polished 'points' with perfectly even faces have been ground; natural faces show tiny growth striations running across the prism.
Rinse in cool water and dry with a soft cloth. Avoid sudden temperature changes, which can open internal fractures.
Quartz has been carved into seals, spheres and reliquary objects for at least four thousand years, and scrying spheres of rock crystal appear in Roman, Japanese and European court collections alike.
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.