[chiralSPO (OP)]

Cinnabar is a beautiful naturally-occurring mineral composed of mercuric sulfide (HgS). There are many examples of jewelry, statues, and even plates made of the stuff, but a quick online search also reveals many pages warning of its unparalleled toxicity (and nearly as many talking about its "crystal healing properties"--ugh I hate that pseudoscience! but I digress...). The only material safety data sheets I have come across do not list any LD50 data. The question is, is cinnabar actually really toxic, or are people just assuming that it is because of the mercury content?

I am well aware of the toxicity of elemental mercury, organometallic mercury compounds, and water-soluble mercury salts, but I also know that actual toxicity is a function of both inherent toxicity and bioavailability. HgS is one of the most water-insoluble compounds: its K_sp is on the order of 10^–54, meaning that a saturated solution in water would only contain about one or two mercury atoms per liter!! And other resources indicate that it will only react with very strong acids to produce soluble species (I wouldn't want to eat it).

Industrially, the compound is roasted to produce sulfur oxides and elemental mercury. So is the toxicity of the mineral due to slow oxidation in the air, leading to production of Hg metal?

[Bored chemist]

It's too insoluble to be very toxic.
However, oxidation can give rise to things like mercury sulphate which is much more soluble.

Reaction with metals could also generate free mercury.

[crissychen]

sounds cool but i have nooo idea how toxic it is lol