Judging quality
Test the color: many blue and green 'calcites' on the market are dyed. Optical clarity, sharp rhombohedral cleavage and a strong fizz in weak acid identify true calcite.
Carbonate
Calcite
One of the most polymorphic minerals known, with hundreds of crystal habits and every color of the spectrum. Optical calcite from Iceland splits an image in two through double refraction.
Care
Soft and acid-sensitive. Keep away from vinegar, citrus and household cleaners; dust dry.
History & lore
Viking navigators may have used Icelandic optical calcite as a 'sunstone' to locate the sun through overcast skies.
Cultural history, recorded as tradition rather than as medical or scientific claim.
Common questions about Calcite
- What is Calcite?
- One of the most polymorphic minerals known, with hundreds of crystal habits and every color of the spectrum. Optical calcite from Iceland splits an image in two through double refraction.
- How hard is Calcite and what is it made of?
- Calcite is a Carbonate-family mineral with the composition CaCO3. It crystallizes in the trigonal system and rates 3 on the Mohs hardness scale. It occurs in orange, honey, green, blue.
- Where does Calcite come from?
- Notable localities for Calcite include Mexico, Brazil, China, Iceland.
- How do you tell good Calcite from filler?
- Test the color: many blue and green 'calcites' on the market are dyed. Optical clarity, sharp rhombohedral cleavage and a strong fizz in weak acid identify true calcite.
- How do you care for Calcite?
- Soft and acid-sensitive. Keep away from vinegar, citrus and household cleaners; dust dry.
See it in person
Photographs only go so far
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.