elements
Mercury
Hg
- Also known as
- quicksilverhydrargyrum
- Crystal system
- trigonal
- Hardness
- 0 on the Mohs scale
- Lustre
- metallic
- Colour
- Silvery liquid
- Where it forms
- As droplets in cinnabar deposits, where mercury sulfide has broken down.
- Chiefly from
- Almaden, SpainIdrija, SloveniaCalifornia, United States
Why it is that colour
Metallic. Mercury is liquid at room temperature for the same relativistic reason gold is yellow: its outer electrons are held so tightly that mercury atoms barely bond to one another.
Safety
A potent neurotoxin in every form, and uniquely hazardous because it evaporates at room temperature — mercury vapour is odourless, and inhaling it is the main route of harm. Organic mercury compounds such as methylmercury are worse still and accumulate in fish. Elemental mercury should never be handled, and a broken thermometer is a genuine cleanup problem rather than a curiosity. It is not sold as a specimen for good reason.
Where it comes from
Mining has been sharply curtailed by the Minamata Convention on Mercury, in force since 2017. Almaden and Idrija, the two great historic mines, are both closed and both UNESCO sites.
Historical use
Used in hat-making — mercuric nitrate treated felt, and the neurological damage it caused in hatters gave English the phrase mad as a hatter. Also used in gold amalgamation, in thermometers, in dental amalgam and in medicine, where mercury compounds were the standard treatment for syphilis for four centuries.
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
Mercury the planet in the alchemical scheme, and the single most important substance in Western and Chinese alchemy alike — a metal that is liquid, that dissolves gold, and that appears to be matter caught between states. Chinese alchemists sought immortality through it and were poisoned by it; European alchemists made it one of the three principles alongside sulfur and salt.
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
Minamata is the reason the convention carries that name. From the 1930s a chemical plant in Minamata, Japan discharged methylmercury into the bay. It concentrated up the food chain into fish, and the fishing community that ate them developed severe neurological damage — loss of coordination, sensory failure, congenital disability in children born to affected mothers. The company and the government resisted acknowledgement for decades, and the photographer W. Eugene Smith's 1970s work on it is among the most consequential photojournalism ever published.
Mercury is in this collection despite not being sold as a crystal, because it is one of the seven alchemical metals, because it explains cinnabar, and because it is the clearest example of a substance whose fascination and whose danger are the same property. It looked like matter in an unfinished state. It was poisoning everyone who studied it.
Identity checked against IMA-CNMNC master list, June 2025.