Judging quality
Look for high-contrast, unbroken chevrons and a good polish that does not undercut the softer white bands.
Quartz
Banded amethyst in which purple and milky white quartz alternate in sharp V-shaped chevrons, recording rhythmic growth along the vein.

Look for high-contrast, unbroken chevrons and a good polish that does not undercut the softer white bands.
Standard quartz care; keep out of long sun exposure.
Much of the material on the market comes from Indian deposits worked since the mid-twentieth century.
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.