The facts
What petoskey Stone actually is
The species behind petoskey Stone is fossil rugose coral in limestone, CaCO₃ replacing Hexagonaria percarinata skeleton; it forms in the aggregate after coral structure system.
Grey to buff carbonate; the hexagonal 'eyes' are the preserved corallites of a Devonian colonial coral is responsible for the colour — and the chromophore, not the name, is what decides whether a colour is stable.
On the instruments it reads a specific gravity of about 2.6–2.8, with rhombohedral cleavage in the calcite cleavage.
Where petoskey Stone comes from
Commercial material comes from Petoskey, Emmet County, Michigan, USA and Charlevoix County, Michigan, USA.
Different localities give different colour and different clarity, and the trade prices them differently. We state which one.
How petoskey Stone is treated
Untreated but soft: the pattern only shows clearly when wet or polished, and many sellers oil or wax dry stones to fake the wet look. Michigan restricts how much may be removed from state land.
We state the treatment on every stone, including when the honest answer is that it cannot be determined. A treatment disclosed is a fact; a treatment discovered later is a refund.
What petoskey Stone is confused with
Watch for Charlevoix stone, Favosite coral and Agatized coral — these are what turn up sold under this name.
Because the material is opaque, refractive index is no help. Specific gravity around 2.6–2.8, hardness of 3.5–4, streak and magnification do the work instead.
What petoskey Stone is used for
The trades that buy petoskey Stone are mineral collecting, jewellery and decorative objects. They do not want the same thing, and they do not pay in the same unit.
We quote each application in the unit that trade actually buys in, by the specimen, by the carat or by the piece.
Durability and care
Petoskey Stone is 3.5–4 on the Mohs scale, with rhombohedral cleavage in the calcite cleavage.
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 petoskey Stone costs
Expect roughly Tumbled stones 5–30 USD; large polished pieces 50–400 USD, depending on quality.
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 petoskey Stone treated, and how?
Untreated but soft: the pattern only shows clearly when wet or polished, and many sellers oil or wax dry stones to fake the wet look. Michigan restricts how much may be removed from state land.
Where does petoskey Stone come from?
Petoskey, Emmet County, Michigan, USA and Charlevoix County, Michigan, USA. Origin affects price, so we name the locality rather than the country on every quote.
Is petoskey Stone hard enough to wear every day?
Not really. At 3.5–4 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 petoskey Stone cost?
Indicatively Tumbled stones 5–30 USD; large polished pieces 50–400 USD. 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 petoskey Stone confused with?
Most often Charlevoix stone, Favosite coral and Agatized coral. Since the material is opaque, separation relies on specific gravity near 2.6–2.8, hardness and magnification.
What is petoskey Stone used for besides jewellery?
mineral collecting and decorative objects. Each of those trades buys it in a different form and a different unit.
Related stones
Looking for petoskey stone?
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 petoskey stone