The facts
What millerite actually is
Mineralogically, millerite is millerite — NiS, crystallising in the trigonal system.
The colour is caused by metallic brass to bronze-yellow, often with an iridescent tarnish on the hair-like crystals. That is worth knowing because it determines what heating, light and time can and cannot do to the stone.
A refractometer gives nothing, because the material is opaque, and the specific gravity sits near 5.3–5.5; cleavage is perfect {1011} and {0112}.
Where millerite comes from
The recognised sources are Halls Gap, Lincoln County, Kentucky, USA, Sterling Mine, Antwerp, New York, USA, Jáchymov, Czech Republic and Wissen, Siegerland, Germany.
Origin affects price in this material, so we name the locality on every quote rather than the country. "African" or "Asian" tells a buyer nothing.
How millerite is treated
Untreated. The golden hair-like sprays inside Kentucky and Wisconsin geodes are extremely fragile and are usually sold sealed under a dome; any brushing destroys them. Occasionally found as inclusions in quartz and marketed as 'golden hair quartz' alongside rutile.
None of this is a problem when it is said out loud. It becomes one the moment it is left out.
What millerite is confused with
The usual confusions are Rutile (in quartz), Pyrite, Chalcopyrite and Gold.
Because the material is opaque, refractive index is no help. Specific gravity around 5.3–5.5, hardness of 3–3.5, streak and magnification do the work instead.
What millerite is used for
Millerite is bought by mineral collecting — and each of those trades wants a different form of the same material.
We quote each application in the unit that trade actually buys in, by the specimen.
Durability and care
Hardness 3–3.5; cleavage perfect {1011} and {0112}. That combination decides what it can safely be set into.
Below about 5.5 a stone will be scratched by ordinary household dust, which is largely quartz. That does not make it unusable — it makes it a pendant, an earring or an object rather than a ring worn every day.
Warm water, mild soap and a soft brush. Avoid ultrasonic cleaners on anything fracture-filled, stabilised, dyed or visibly included.
What millerite costs
Indicative pricing for millerite is Geode specimens $30–$1,500.
That is a range, not a quote. Colour, size, clarity, cut and origin move the figure a long way inside it, and the only honest price is one given against a specific stone. Send us what you need and we will price it.
Questions
Is millerite treated, and how?
Untreated. The golden hair-like sprays inside Kentucky and Wisconsin geodes are extremely fragile and are usually sold sealed under a dome; any brushing destroys them. Occasionally found as inclusions in quartz and marketed as 'golden hair quartz' alongside rutile.
Where does millerite come from?
Halls Gap, Lincoln County, Kentucky, USA, Sterling Mine, Antwerp, New York, USA, Jáchymov, Czech Republic and Wissen, Siegerland, Germany. Origin affects price, so we name the locality rather than the country on every quote.
Is millerite hard enough to wear every day?
Not really. At 3–3.5 on the Mohs scale it is softer than the quartz dust in ordinary household dirt, so it scratches with wear. It suits pendants, earrings and objects better than a daily ring.
How much does millerite cost?
Indicatively Geode specimens $30–$1,500. Colour, size, clarity and origin move the price a long way within that, so treat it as a range and ask for a quote against a specific stone.
What is millerite confused with?
Most often Rutile (in quartz), Pyrite, Chalcopyrite and Gold. Since the material is opaque, separation relies on specific gravity near 5.3–5.5, hardness and magnification.
Related stones
Looking for millerite?
Tell us the size, the quality and what it is for. We source it, photograph it and quote it — with the locality named.
Ask about millerite