Is realgar safe to handle
Realgar is 70.03% arsenic by mass and hardness 1.5 to 2. The risk is not touching it: it turns itself into arsenic-rich powder in light, without being handled.
Realgar is arsenic sulphide, AsS, and 70.03% arsenic by mass against arsenopyrite's 46.01%. An intact crystal handled briefly with clean dry hands is the low-risk case. The real hazard is that the Handbook of Mineralogy records realgar as disintegrating on long exposure to light into a powder of pararealgar, arsenolite and orpiment. The specimen makes its own dust.
In short
- The question has the wrong verb. Handling is not the exposure route that matters. A realgar crystal left in light breaks down on its own into a loose powder, and powder is what gets onto hands, into a drawer and into the air. A specimen you never touch can still be the problem.
- Realgar is 70.03% arsenic by mass, calculated from AsS with a formula mass of 106.98. For comparison, orpiment is 60.91% and arsenopyrite 46.01%. Among the primary arsenic minerals a collector meets it is the richest in arsenic; only its own decay products go further, arsenolite at 75.74% by mass and pararealgar at hardness 1 to 1.5.
- The breakdown product is more arsenic-rich than the mineral, and it is soluble. Arsenolite, As2O3, is 75.74% arsenic and an oxide rather than a sulphide, so it behaves quite differently around water. Of 158 Handbook species sheets in this site's reference set, exactly one uses the word toxic — arsenolite's, which reads a very toxic substance.
- Light is the trigger, and the conservation literature says so plainly. The NatSCA guidance names the arsenic sulphides as the most susceptible group to light damage, realgar specifically, and recommends light-proof containers. A sealed opaque box is not a precaution for the collector; it is a precaution for the specimen.
- Nothing on this page is health, safety or legal advice. Occupational arsenic exposure is governed by EH40 and the COSHH Regulations 2002, and anything beyond the mineralogy belongs with them or with an occupational hygienist, not with a mineral reference page.
| Species | Formula | Arsenic by mass | Hardness | State it arrives in |
|---|---|---|---|---|
| Realgar | AsS | 70.03% | 1.5 to 2 | Red to orange-red crystals to 12 cm; sectile, resinous |
| Pararealgar | As4S4 | 70.03% | 1 to 1.5 | Bright yellow when powdery. Approved as a species in 1980; the commonest decay product |
| Arsenolite | As2O3 | 75.74% | 1.5 | White octahedra or bloom. The one sheet in 158 the Handbook calls a very toxic substance |
| Orpiment | As2S3 | 60.91% | 1.5 to 2 | Lemon-yellow foliated masses; perfect {010} cleavage, flexible lamellae |
| Arsenopyrite | FeAsS | 46.01% | 5.5 to 6 | Silver-white prisms. Hard, stable in light, and a different problem entirely |
What the reference sheets actually record, and the arithmetic behind the numbers
Method, so the figures can be checked. The mass fractions above are calculated from the ideal formula using standard atomic weights — arsenic 74.9216, sulphur 32.06, oxygen 15.999, iron 55.845. Realgar, AsS, has a formula mass of 106.98, of which arsenic is 74.9216, giving 70.03%. Arsenolite, As2O3, has a formula mass of 197.84, of which arsenic is 149.84, giving 75.74%. No source is being paraphrased; the numbers are arithmetic on a formula.
The Handbook of Mineralogy sheet for realgar carries the decisive sentence in its physical-properties block, immediately after the density: Disintegrates on long exposure to light to a powder composed of pararealgar or arsenolite and orpiment. Across the 158 sheets in this site's reference set, six mention exposure to light at all — baryte, chlorargyrite, pararealgar, proustite, pyrargyrite and realgar — and realgar's is the only one that describes the specimen turning into powder rather than merely changing colour.
The second finding is the one that surprised us. Counting every occurrence of the word toxic across all 158 sheets returns exactly one hit. It is on arsenolite, and it reads Taste astringent, sweetish; a very toxic substance. The Handbook is a descriptive mineralogical reference that does not issue hazard warnings, about uraninite, about cinnabar, about autunite or about realgar itself. It made one exception, and it made it for the thing realgar becomes.
Why this is a different page from the arsenopyrite one
This site already covers whether arsenopyrite is dangerous, and the honest answer there is that arsenopyrite is a hard, stable, unreactive species whose arsenic is locked in a sulpharsenide lattice. Realgar is the opposite mineral on every axis that matters.
Hardness 1.5 to 2 against 5.5 to 6. Arsenopyrite resists a steel point; realgar is softer than a fingernail and the Handbook records it as sectile. It abrades against anything it is stored with.
Good cleavage on {010} against no cleavage worth the name. Realgar parts along a plane, so a knock does not chip it, it splits it.
Stable in light against not stable in light. This is the whole difference. Arsenopyrite on an open shelf in 1950 is arsenopyrite today. Realgar on an open shelf in 1950 is a heap of orange-yellow powder with a label next to it, and every curator who has opened a Victorian cabinet has seen one.
So the reasonable precautions differ. For arsenopyrite the rule is do not grind it and wash your hands. For realgar the rule is a sealed, opaque, labelled container, opened rarely, and the recognition that the specimen is consuming itself whether or not you touch it. The general group is covered on toxic minerals in a collection.
How to store one, and what it costs to do properly
The NatSCA guidance on the care and conservation of geological specimens states that light will irreversibly damage some mineral species, names the arsenic sulphide group as the most susceptible, cites realgar explicitly for its irreversible reaction to light, and recommends that susceptible species be stored in light-proof containers. That is the standard, and it is a museum standard rather than a counsel of perfection.
What it takes, honestly. A rigid opaque box with a gasket or a tight lid. Inert padding — closed-cell polyethylene foam or acid-free tissue, not cotton wool, which sheds and catches on a sectile mineral. A written label on the outside of the box as well as inside it, because the next person to open it may not be you. A drawer rather than a shelf. And a decision never to display it, which for a mineral this colour is the part people actually resist.
None of that is expensive and all of it is fiddly, which is the honest cost: the barrier to storing realgar properly is attention, not money. The related storage cases are covered on how to store soluble mineral specimens, which minerals fade in light and handling and storage, and the rest of this section is indexed at the collecting guides.
If the answer you reach is that you would rather not keep one, that is a defensible answer and a common one. We hold no catalogue and nothing on this site is offered for sale; the wanted list sets out what we look for, and we do not seek material that cannot be stored safely. Where a collection needs rehousing rather than dispersing, a conservator is the right call and we will say so.