Turquoise or Dyed Howlite: How to Tell Them Apart Safely

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White howlite, which is very porous, is dyed blue to imitate turquoise. Here are the signs, the safe tests and the label terms so you do not get it wrong.

Key points

Turquoise	Hydrated copper aluminium phosphate, hardness 5 to 6, density 2.6 to 2.9
Howlite	Hydrated calcium borosilicate, hardness 3.5, density 2.5 to 2.6
Common practice	White howlite (or magnesite) dyed blue and sold under names close to “turquoise”
Other cases	Turquoise stabilised with resin, treated, reconstituted into blocks, glass, plastic
Typical sign	Blue that is too uniform, darker tint in the cracks, drawn-on grey or black veins
Safe test	Loupe, a slightly damp white cotton cloth on an inconspicuous area, weight, reading the description

Two stones that could not be more different

Turquoise is a hydrated phosphate of copper and aluminium, with the formula CuAl6(PO4)4(OH)8·4H2O. Its Mohs hardness is 5 to 6 and its density 2.6 to 2.9. Its colour, from sky blue to blue-green, comes from copper (the blue) and iron (the green tendency). It forms in the weathered zones of rocks rich in aluminium and copper, in a rather dry climate. Historic deposits include Iran (Nishapur), Sinai, China (Hubei) and the United States (Arizona and Nevada, today among the main producers).

Howlite is a white mineral, a calcium borosilicate with the formula Ca2B5SiO9(OH)5, formed in evaporite-type deposits. Its hardness is 3.5 and its density around 2.5 to 2.6. It is naturally white, with grey or black veinlets. This pattern resembles the “matrix” of some turquoises, and its porosity lets it absorb dyes easily. Once dyed blue, it becomes a very widespread imitation, sometimes sold under the trade name “turquenite” (a commercial name for howlite, or magnesite, coloured blue).

So there is one point to understand clearly: dyed howlite is not fake stone in the sense of artificial material. It is genuine howlite. What is misleading is the name or the colour that suggests turquoise.

The table of signs

Sign	Natural turquoise	Dyed howlite or magnesite
Colour	Sky blue, blue-green, green; variations within a single piece	Intense, very uniform blue, sometimes “swimming-pool blue” or “neon blue”
Veins	Brown, black, golden or grey matrix, natural and irregular in shape	Very sharp grey or black veins on a flat blue background, sometimes too regular
Cracks and cavities	Same shade as the rest of the stone	Darker tint building up in cracks and hollows; white visible inside a chip
Lustre	Waxy to matt, silky after polishing	Matt to vitreous, sometimes powdery
Weight	A little denser, a little heavier in the hand	A little lighter (howlite); magnesite is rather a little heavier than howlite
Hardness	5 to 6: does not scratch easily	3.5: scratches easily with a metal object
Exposure to moisture	Stays stable (except unstabilised porous pieces)	May bleed colour onto a damp white cotton cloth

Turquoise blue is never “perfect”: its irregularity is exactly what gives it away. A completely uniform, saturated blue on a large, inexpensive piece should make you hesitate.

Simple, safe tests

Read the description and the label. Look for the words “dyed”, “tinted”, “stabilised”, “reconstituted”, “howlite”, “magnesite”. A name such as “synthetic turquoise” or “turquoise blue” does not tell you what the material is.
Look under a loupe at the cracks and cavities. A dyed stone shows a coloured rim inside the fissures and white areas where the dye has not penetrated.
Rub a slightly damp white cotton cloth, using only lukewarm water, on an inconspicuous area (under a setting, on the back of a bead). If the cotton turns blue, the piece is dyed. If nothing comes off, that does not prove it is not dyed: some dyes are resistant.
Compare the weight and the feel with a piece whose nature is known: turquoise feels cool and is a little heavier than howlite.
Look at the shape of the veins: on turquoise, the matrix follows the natural forms of the rock; on a dyed piece, it resembles the original howlite, with its characteristic grey lines.

Avoid: acid, fire, acetone and a heated needle. A hot-needle test, sometimes recommended, is used to detect the smell of plastic, but it leaves a mark and gives off irritating fumes; it is only justified in a laboratory. Also avoid scratching the piece: the difference in hardness is real (3.5 against 5 to 6), but the test leaves a trace.

What these tests cannot prove. Turquoise impregnated with resin (stabilised), reconstituted turquoise or a well-made plastic imitation easily pass these checks. For a valuable piece, a certificate from a gemmological laboratory is the only reliable way to know.

Natural turquoise does not mean untreated

Even among genuine turquoises, several situations coexist. Turquoise is a porous stone, often chalky when mined, and much of what is sold has been treated:

Untreated natural turquoise: rare in jewellery-grade quality, it is hard and takes a fine polish by itself. It may darken over time with contact with skin and cosmetics.
Stabilised turquoise: the soft material is impregnated with an epoxy resin, a plastic or sodium silicate to harden it and fix the colour. It remains basically natural turquoise, but the treatment must be disclosed.
“Zachery” treated turquoise: a commercial process patented in the 1980s, which improves stability and sometimes colour.
Reconstituted turquoise (“block”): powder or small fragments glued together with a resin. Depending on the sources, it may contain very little actual turquoise.
Synthetic turquoise: laboratory products exist. They have a composition close to turquoise without being natural.

The French decree no. 2002-65 of 14 January 2002 requires dyeing to be declared; it does not necessarily require every traditional treatment, such as oil or wax, to be mentioned. All the more reason to ask the seller.

Misleading names and words to watch

What the label says	What it may cover
Turquoise	Should mean genuine turquoise, possibly stabilised; check the treatment disclosure
Turquenite, “turquoise” howlite, “turquoise magnesite”	Dyed howlite or magnesite, not turquoise
Reconstituted turquoise, “block”, “pressed”	Turquoise powder glued with a resin
Synthetic or “laboratory” turquoise	Manufactured material with a composition close to turquoise
Turquoise “from China”, “from Arizona”, “Tibetan”	Origins that are sometimes commercial; ask with caution, without certainty
Blue stone	Too vague a term: may mean sodalite, amazonite, chalcedony or glass

What to do if you already own a doubtful piece

A piece of dyed howlite is neither dangerous nor without decorative value: it is a lovely blue object, as long as you know what it is. A few care precautions follow from this. Avoid hot water, prolonged sunlight and household products, which can make the colour bleed. Do not wear it in the shower, at the swimming pool or at the sea. Store it apart from light-coloured stones: dye that runs can stain.

If you bought a piece presented as natural turquoise and you have doubts, write to the seller asking for the exact nature of the material; for a distance purchase, you generally have fourteen days to exercise your right of withdrawal. To understand the wording on a label, read our page on treated stones. For the symbolic profile of the stone, see turquoise and howlite.

Frequently asked questions

How can I recognise howlite dyed blue?

Look for a blue that is too uniform, a darker colour in the cracks, white visible inside a chip and very sharp grey veins. A damp white cotton cloth may sometimes take on colour. The piece is also softer (hardness 3.5).

Is dyed howlite fake turquoise?

It is genuine howlite, a natural mineral, coloured to resemble turquoise. It should not be sold as turquoise. It is not dangerous, but its colour may bleed.

What is turquenite?

It is a trade name given to howlite (or magnesite) dyed blue. There is no mineral called turquenite.

Is stabilised turquoise fake?

No, it is natural turquoise hardened with a resin or another product. The treatment must be disclosed. It differs from reconstituted turquoise, which is made of glued powder.

Can I test turquoise with a hot needle or acid?

No. These tests leave marks, give off irritating fumes or destroy the stone. Prefer a loupe, touch, weight and reading the description, and a laboratory if in doubt.