Can I really not wash selenite?

Correct. Gypsum is soluble enough that running water will dull a polished surface and repeated washing will visibly erode it. Soaking is worse. Dust it with a dry cloth or a soft brush. The widespread advice to cleanse selenite in water is one of the clearest cases of a modern practice damaging the stone it is applied to.

Is my selenite wand actually selenite?

Probably satin spar, which is the fibrous form of the same mineral, gypsum. The trade calls both selenite and nobody is being deceived. Proper selenite is the transparent bladed material; satin spar has a silky chatoyant sheen along its length. Care is identical for both.

Why does fluorite chip so easily at hardness 4?

Because hardness and toughness are different properties. Fluorite has perfect cleavage in four directions, following the faces of an octahedron, so a knock in any of those directions splits it cleanly regardless of how well it resists scratching. Many fluorite octahedra sold as natural crystals were in fact cleaved into that shape.

A banded purple and cream fluorite from Castleton in Derbyshire, mined since the eighteenth century for decorative vases and inlay. It is almost certainly the murrine that Roman writers describe as being made into extraordinarily expensive cups. Very little is now extracted, and genuine antique pieces are valuable.

Are these stones safe to handle?

Yes. Gypsum, celestite and fluorite are not toxic in ordinary handling, and gypsum is the same material as plasterboard. As with any mineral, do not grind or sand them without dust control, and do not put them in drinking water, in this case because they will partly dissolve rather than because they will poison you.

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Mineral family

Evaporites & halides

The most fragile family in the catalogue, and the one most damaged by well-meaning owners. These stones formed where water dried out or cooled, and the practices most commonly recommended for them, washing and sun-charging, are precisely the two things that destroy them.

At a glance

Selenite, celestite and fluorite formed as water evaporated or as fluids cooled. Several of them will go back into water if you give them the chance.

Keynote: Stones that crystallised out of drying water
Chemistry: sulfates & halides
Crystal systems: Monoclinic, orthorhombic & cubic
Mohs range: 2 to 4
Stones here: 3 in the catalogue
Care rule: Never water. Never sunlight for fluorite and celestite. Never dropped, for anything with cleavage this perfect.
Watch for: Selenite sold for water cleansing; dyed and heat-treated fluorite.

Themes

clearing stillness order the crystal from drying water fragility what light undoes

What holds the family together

Selenite is gypsum, calcium sulfate dihydrate, at hardness 2, which means a fingernail marks it. It is mildly soluble in water: not dramatically, but a polished piece washed regularly will dull and lose its edges, and left soaking it will visibly deteriorate. The satin spar sold as selenite wands is the fibrous form, and the transparent bladed material is proper selenite. Both are gypsum.

The Naica cave in Mexico contains selenite crystals up to eleven metres long, the largest natural crystals ever found, which grew over hundreds of thousands of years in mineral-saturated water held at a constant temperature.

Celestite is strontium sulfate at 3.5, usually sold as hollow geodes from Madagascar lined with pale blue crystals. It is brittle, cleaves easily, and fades in sunlight.

Fluorite is calcium fluoride at 4, cubic, with perfect cleavage in four directions. It gave fluorescence its name, because many specimens glow under ultraviolet light, and it is the reason the phenomenon has that word at all.

How it forms

Gypsum forms where seawater or saline lake water evaporates, leaving beds of sulfate that can be hundreds of metres thick. The great gypsum deposits of the Mediterranean formed when the sea largely dried out around six million years ago.

Celestite forms in sedimentary rocks, often in geodes within limestone, and Madagascar supplies most decorative material.

Fluorite forms in hydrothermal veins, frequently with lead and zinc ores, and it occurs worldwide. The Blue John of Castleton in Derbyshire, banded purple and cream, was mined from the eighteenth century and was almost certainly the murrine that Roman writers describe being made into extremely costly cups.

China now supplies the bulk of the world's fluorite, both for industry, where it is the main source of fluorine, and for specimens.

The stones of this family

Selenite (CaSO₄·2H₂O, Mohs 2). Gypsum in its clear bladed form, named for the moon, soft enough to scratch with a fingernail and destroyed by water. The Naica cave crystals are eleven metres long.
Celestite (SrSO₄, Mohs 3.5). Pale blue strontium sulfate, usually sold as hollow geodes from Madagascar. Fragile, light-sensitive and one of the few genuinely blue minerals in nature.
Fluorite (CaF₂, Mohs 4). The stone that gave fluorescence its name, and the Blue John of Derbyshire that Rome imported as murrine cups. Perfect octahedral cleavage makes it fragile.

Trade names and lookalikes

Selenite is the family's naming problem rather than a fraud problem. Almost everything sold as a selenite wand or tower is satin spar, a fibrous gypsum, and calling it selenite is standard trade usage rather than deception. Genuine clear bladed selenite is also common and inexpensive.

Fluorite is dyed and heated to enhance colour, and coated fluorite exists. Natural fluorite runs purple, green, blue, yellow and colourless, often in bands, and the very saturated single-colour material at low prices is often treated.

Celestite is rarely faked but is regularly mislabelled as celestine, which is simply the alternative name for the same mineral.

Watch for hollow geodes with crystals glued in, which happens with several materials at the cheap end of the market.

Care that follows from the structure

This family needs three rules kept absolutely.

No water. Selenite dissolves. Celestite is damaged. Fluorite is less soluble but its cleavage means water in a crack plus a temperature change can split it. Dust with a dry soft brush.

No sunlight. Fluorite and celestite both fade, sometimes noticeably within months on a bright windowsill.

No impact. Fluorite cleaves perfectly in four directions, so a knock on a corner takes a clean triangular chip off. Celestite crumbles. Selenite at hardness 2 scratches on almost anything, including being slid across a wooden shelf.

None of these should be worn as jewellery in any working context, and none should be used for gem waters by direct contact. If you want to keep a fluorite octahedron intact, keep it in a lined box.

Spørsmål til refleksjon

What am I looking after by habit rather than by the object's actual needs?
Where does a practice I inherited actively damage the thing it claims to serve?
What in my life is beautiful precisely because it will not last?

Stones in this family

⚪

Selenite

Gypsum, moon-named, destroyed by water

🔵

Celestite

Pale blue geodes, brittle and fading

🟣

Fluorite

Octahedra, Blue John, and the source of the word fluorescence

⚪

The clear & white ray

Where selenite sits

🟣

The violet ray

Where most fluorite sits

Frequently asked questions

: Correct. Gypsum is soluble enough that running water will dull a polished surface and repeated washing will visibly erode it. Soaking is worse. Dust it with a dry cloth or a soft brush. The widespread advice to cleanse selenite in water is one of the clearest cases of a modern practice damaging the stone it is applied to.
: Probably satin spar, which is the fibrous form of the same mineral, gypsum. The trade calls both selenite and nobody is being deceived. Proper selenite is the transparent bladed material; satin spar has a silky chatoyant sheen along its length. Care is identical for both.
: Because hardness and toughness are different properties. Fluorite has perfect cleavage in four directions, following the faces of an octahedron, so a knock in any of those directions splits it cleanly regardless of how well it resists scratching. Many fluorite octahedra sold as natural crystals were in fact cleaved into that shape.
: A banded purple and cream fluorite from Castleton in Derbyshire, mined since the eighteenth century for decorative vases and inlay. It is almost certainly the murrine that Roman writers describe as being made into extraordinarily expensive cups. Very little is now extracted, and genuine antique pieces are valuable.
: Yes. Gypsum, celestite and fluorite are not toxic in ordinary handling, and gypsum is the same material as plasterboard. As with any mineral, do not grind or sand them without dust control, and do not put them in drinking water, in this case because they will partly dissolve rather than because they will poison you.

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Mineralfamiliene

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