Gem library
Angelite
The blue anhydrite of Peru
Angelite is anhydrite, a calcium sulphate deprived of water. Its best-known relative is gypsum, which is exactly the same compound but hydrated: the difference comes down to two water molecules, and it changes everything, including how the stone must be kept.
- Hardness (Mohs)
- 3 – 3.5
- Density
- 2.90 – 3.00
- Crystal system
- Orthorhombic
- Refractive index
- 1.570 – 1.614
- Cleavage
- Perfect on {010}
Mineralogical identity
- Family
- Sulphates
- Species
- Anhydrite
- Variety
- Compact blue anhydrite
- Chemical formula
- CaSO₄
- Crystal system
- Orthorhombic
- Classification
- Ornamental stone (rock)
- Rarity
- Common
- Indicative price
- €0.20 – 3/ct
Etymology
A trade name created in the 1980s by analogy with angels, for its pale blue colour. The mineralogical name, anhydrite, comes from the Greek and means «without water».
Physical & optical properties
- Hardness (Mohs)
- 3 – 3.5
- Density
- 2.90 – 3.00
- Refractive index
- 1.570 – 1.614
- Birefringence
- 0.044
- Cleavage
- Perfect on {010}, distinct on {100} and {001}
- Fracture
- Uneven
- Lustre
- Matt to vitreous
- Diaphaneity
- Opaque
- UV fluorescence
- None
- Pleochroism
- None
- Colours
- pale blue, blue grey, lavender, white
Formation, geology & history
Without water, and that is the whole problem
Anhydrite is anhydrous calcium sulphate, CaSO₄. Add two water molecules and you get gypsum, CaSO₄·2H₂O, whose crystallised variety is selenite. The transformation runs both ways depending on temperature and humidity: above about sixty degrees, gypsum loses its water and becomes anhydrite; in water at room temperature, anhydrite takes it back and becomes gypsum again. That reaction comes with an increase in volume of about sixty percent, and it is what makes certain ground swell and cracks tunnels dug in anhydrite. For a stone sitting on a shelf the consequence is simple: water destroys it, slowly but surely.
Where the blue comes from
Anhydrite deposits are evaporites, formed by the drying out of marine basins. Most are white, grey or pinkish. The lavender-blue material from Peru, the only kind worked for ornament, owes its tint to metallic traces and to its microcrystalline texture, which scatters light. It arrives as compact blocks that are cut into spheres, pyramids and little angels, the shape that gave the trade name. The material is soft, it turns and polishes easily, and it takes a characteristic satin finish, slightly matt, very different from the brilliance of a hard stone.
One family, three shop names
The trade in pale blue stones keeps up a certain confusion. Angelite is anhydrite, opaque and matt. Celestite is a strontium sulphate, translucent and crystallised in geodes. Larimar is a pectolite from the Caribbean, sky blue veined with white, distinctly harder. The three look alike from a distance, sell at very different prices and have nothing in common but the colour. Weight settles it quickly: celestite, at 3.97, is far heavier than angelite, at 2.95.
How to recognise it
- The satin feelThe polished surface stays slightly matt, velvety, without the vitreous lustre of a hard stone. That is characteristic of compact anhydrite.
- Hardness 3A copper coin scratches it, a fingernail almost marks it. A pale blue stone that resists steel is not angelite.
- The water dropPut a drop on a hidden area and leave it a minute: the surface dulls locally. The test is conclusive but it damages, so keep it as a last resort.
Imitations, treatments & confusions
- Howlite dyed blueThe dominant imitation. It has characteristic black veins that angelite does not have, and the dye concentrates in them.
- Ceramic and dyed pasteOn cheap little angels. Too regular, sometimes a mould line, and a clear ring when tapped.
- Blue calciteA real stone but another species. It fizzes in dilute acid, anhydrite does not.
Deposits & origins
Peru (the only deposit of ornamental material), Mexico, Germany, Poland, Italy, United States
Care & precautions
- Never water, in any form. Anhydrite rehydrates, swells and falls apart. That is the most important point on this page.
- A soft dry cloth, nothing else.
- Avoid damp rooms, bathroom included: ambient humidity alone is enough to dull it over a few years.
- Store isolated, at hardness 3 it is scratched by just about anything.
Traditions & crystal healing
- Chakras
- Throat · crown
- Zodiac signs
- Aquarius · Pisces
- Element
- Air
A stone of gentleness and calmed speech, strongly associated with communication and connection, and readily carved into angel figurines, which gave it both its name and its reputation. Cultural heritage, never medicine.
The virtues described here belong to tradition and cultural heritage. They are in no way medical advice and never replace a consultation.
Frequently asked questions
Can an angelite be cleansed in water?
No, and this is the stone on which that common advice does the most damage. Water chemically transforms it into gypsum and breaks it up.
Angelite or celestite?
Weight. Celestite, a strontium sulphate, weighs 3.97 against 2.95: at equal volume the difference is obvious in the hand. Celestite is also translucent and crystallised, angelite opaque and matt.
Why has my stone turned whitish?
It has hydrated at the surface. That is irreversible for the polish. Keep it dry and away from the bathroom.
Tools for this stone
Angelite: only the tools this stone actually concerns, each carrying the value read on this page.