silicates
Epidote
Ca2(Al2Fe3+)[Si2O7][SiO4]O(OH)
- Also known as
- pistaciteunakite
- Crystal system
- monoclinic
- Hardness
- 6–7 on the Mohs scale
- Lustre
- vitreous
- Colour
- Pistachio green to greenish black
- Where it forms
- In regionally metamorphosed rocks and in hydrothermally altered igneous rock, which is where unakite comes from.
- Chiefly from
- Knappenwand, AustriaPakistanMaliAlaska, United States
Why it is that colour
Iron. The yellowish-green is distinctive enough to be called epidote green.
Safety
Safe to handle.
Where it comes from
Common. The Knappenwand locality in Austria produced classic specimens in the nineteenth century.
Historical use
Geologically significant as an indicator of specific metamorphic and alteration conditions; of no historical economic importance.
Recorded as history and attributed where possible. That a stone was used for something establishes that people used it, not that it worked.
What is attributed to it, and since when
No traditional attribution. Named in 1801 from the Greek for increase, referring to a crystallographic feature. Modern meanings are recent.
Described, not endorsed. Dating a claim is not the same as assessing it — but an association that first appears in a book published in 1985 is not an ancient inheritance, whatever the label says. A sincere account of feeling better is compatible with the stone doing nothing — see the placebo effect.
Worth knowing
Epidote is here mainly because it is half of unakite, and because it is one of the minerals that tells geologists a rock has been through hot water. Epidote in a granite means the rock was altered after it formed, and mapping where epidote appears maps where the fluids went.
It is a working mineral. Nothing about it is rare or valuable, and it is in this collection for what it indicates rather than what it is.
Identity checked against IMA-CNMNC master list, June 2025.