Gem library
Magnesite
The veined white stone dyed turquoise
Magnesite is a white stone run through with grey veins that looks a great deal like howlite. It is best known for what is done with it: dyed, it becomes the most widespread fake turquoise in the world, and it is worth knowing how to recognise.
- Hardness (Mohs)
- 3.5 – 4.5
- Density
- 2.98 – 3.02
- Crystal system
- Trigonal
- Refractive index
- 1.509 – 1.717
- Cleavage
- Perfect on {1011}
Mineralogical identity
- Family
- Carbonates, calcite group
- Species
- Magnesite
- Variety
- Compact magnesite
- Chemical formula
- MgCO₃
- Crystal system
- Trigonal (rhombohedral)
- Classification
- Collector's mineral · ornamental stone
- Rarity
- Very common
- Indicative price
- €0.05 – 2/ct
Etymology
From Magnesia, a region of Thessaly in Greece, which also gave its name to magnesium, to magnetite and to the magnet.
Physical & optical properties
- Hardness (Mohs)
- 3.5 – 4.5
- Density
- 2.98 – 3.02
- Refractive index
- 1.509 – 1.717
- Birefringence
- 0.191
- Cleavage
- Perfect on {1011}, rhombohedral
- Fracture
- Conchoidal
- Lustre
- Vitreous to matt
- Diaphaneity
- Opaque to translucent
- UV fluorescence
- Weak
- Pleochroism
- None
- Colours
- white, cream, grey, light brown
Formation, geology & history
Formation and geology
Magnesite is magnesium carbonate, a direct relative of calcite whose structure it shares. It forms in two ways: by alteration of magnesium-rich ultrabasic rocks, the serpentinites, where it fills veins and honeycomb networks; or by replacement of limestones in contact with magnesian fluids. The ornamental material comes mainly from Bahia, in Brazil, as compact white masses run through with grey to brown veinlets. By tonnage, magnesite is first of all a major industrial mineral: calcined, it gives the refractory magnesia that lines steel furnaces, and it is one of the sources of magnesium metal.
Dyeing, and why it works so well
Compact magnesite is porous and pale: it drinks dye like blotting paper and holds it throughout. Dyed blue-green, it imitates turquoise convincingly, the grey veins playing the part of the matrix. Dyed red, it imitates coral; purple, sugilite; green, malachite or chrysoprase. A considerable share of the cheap «turquoise» and «coral» on the world market is dyed magnesite, often without the seller himself knowing. It is not illegal as long as it is declared, and it is an honest material when sold for what it is.
Telling it from howlite
Magnesite and howlite resemble each other to the point of being interchangeable in the trade, and most shops confuse them. Both are white, veined, soft and porous. Howlite is a calcium borosilicate, hardness 3.5, with crisp, clearly drawn black veins. Magnesite is a carbonate, a little harder, with more diffuse brownish veins. The decisive test is acid: a drop of warm vinegar or dilute acid fizzes on magnesite, not on howlite. In practice the difference has hardly any consequence, both being used for the same purposes.
How to recognise it
- Effervescence in acidA drop of warm white vinegar on a hidden area makes magnesite fizz. Howlite stays silent. It is the only test that really settles it.
- Diffuse veinsIn magnesite the veins are blurred, brownish, and blend into the mass. In howlite they are black and crisp, as if drawn in ink.
- PorosityA drop of water soaks in and darkens the surface within seconds. A genuine turquoise, being denser, reacts far less.
Imitations, treatments & confusions
- Dyed magnesite sold as turquoiseThe reverse of the usual problem: here magnesite is the imitation. Rub a hidden corner with cotton soaked in acetone, and the dye bleeds.
- Dyed magnesite sold as coral or sugiliteSame process, other colours. Too uniform a red or purple on a soft, veined stone should raise the alarm.
- Reconstituted pasteMagnesite powder bound with resin. Too homogeneous a mass, no natural veins, and it does not fizz where the resin covers it.
Deposits & origins
Brazil (Bahia, the ornamental material of the trade), Austria (Styria), China, Greece, Russia, Australia, United States
Care & precautions
- No water: porous and carbonate, it absorbs and dulls. A soft dry cloth.
- Never an acid product, even a mild one: vinegar and lemon attack it.
- Dyed stones fade in sunlight, keep them in the shade.
- Store separately, at hardness 4 it is scratched by just about anything.
Traditions & crystal healing
- Chakras
- Crown · third eye
- Zodiac signs
- Aries · Taurus
- Element
- Earth
A stone of relaxation and letting go, much used in bracelet beads, often presented in connection with magnesium and muscular relaxation. Honesty requires saying that the magnesium in a solid carbonate is not absorbed through the skin, and the link is an image. 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
Is my turquoise dyed magnesite?
Possibly, especially if it was cheap. Cotton with acetone on a hidden corner: if the dye comes away, that settles it. A drop of vinegar that fizzes confirms the carbonate.
Magnesite or howlite?
Acid settles it: magnesite fizzes, howlite does not. Visually, diffuse brown veins on one side, crisp black veins on the other.
Can it go in water?
No. It is porous and it is a carbonate: water dulls it and slightly acid water attacks it.
Tools for this stone
Magnesite: only the tools this stone actually concerns, each carrying the value read on this page.