The facts
What orthoceras actually is
Orthoceras is classified as devonian nautiloid cephalopod shells preserved in a black bituminous limestone, cut and polished as slabs, with the composition Calcite CaCO3 in a bituminous limestone matrix. It crystallises in the aggregate (trigonal calcite) system.
Colour comes from organic carbon and bitumen give the black matrix; the shells appear as pale calcite, which is also what a laboratory looks at when it is asked whether a colour is natural.
Refractive index 1.486-1.658. Specific gravity around 2.6-2.8. Cleavage: calcite rhombohedral cleavage in the crystalline fill. Those three numbers separate it from most of what imitates it.
Where orthoceras comes from
Orthoceras is produced at Erfoud and Alnif, Tafilalt, Morocco - essentially the world's sole commercial source and Atlas Mountains quarries, Morocco.
The locality is part of the description, not a footnote — two stones of the same weight from two of these places are not the same stone.
How orthoceras is treated
Heavily worked: shells are frequently carved, deepened or wholly engraved into the slab to improve the pattern, and the slabs are resin-filled and waxed. A high proportion of decorative tables and sinks contain at least partly artificial fossils. Moroccan fossil export requires permits under the 2015 Mining Code that are commonly not obtained. Genuine specimens show irregular natural spacing and broken sections; too-perfect, evenly-spaced cones are carved.
Treatment changes value, sometimes by a multiple, so it belongs in the description before the price and not after the sale.
What orthoceras is confused with
In the trade orthoceras is most often mistaken for, or substituted by, Carved or engraved fake cones in real limestone, Cast resin panels or Belemnites.
The separation is rarely a matter of opinion: refractive index 1.486-1.658 and specific gravity 2.6-2.8 settle most of it in a minute, and magnification settles the rest.
What orthoceras is used for
Demand for orthoceras comes from architecture and interiors, decorative objects and mineral collecting, which is why one price per carat never covers it.
We quote each application in the unit that trade actually buys in, by the square metre, by the piece or by the specimen.
Durability and care
Orthoceras is 3-4 on the Mohs scale, with calcite rhombohedral cleavage in the crystalline fill 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 orthoceras costs
As a guide, orthoceras trades around $20-200 for small polished plates; tables and sinks $300-3,000.
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 orthoceras treated, and how?
Heavily worked: shells are frequently carved, deepened or wholly engraved into the slab to improve the pattern, and the slabs are resin-filled and waxed. A high proportion of decorative tables and sinks contain at least partly artificial fossils. Moroccan fossil export requires permits under the 2015 Mining Code that are commonly not obtained. Genuine specimens show irregular natural spacing and broken sections; too-perfect, evenly-spaced cones are carved.
Where does orthoceras come from?
Erfoud and Alnif, Tafilalt, Morocco - essentially the world's sole commercial source and Atlas Mountains quarries, Morocco. Origin affects price, so we name the locality rather than the country on every quote.
Is orthoceras hard enough to wear every day?
Not really. At 3-4 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 orthoceras cost?
Indicatively $20-200 for small polished plates; tables and sinks $300-3,000. 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 orthoceras confused with?
Most often Carved or engraved fake cones in real limestone, Cast resin panels and Belemnites. A refractive index of 1.486-1.658 and a specific gravity near 2.6-2.8 separate it quickly.
What is orthoceras used for besides jewellery?
architecture and interiors, decorative objects and mineral collecting. Each of those trades buys it in a different form and a different unit.
Related stones
Looking for orthoceras?
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 orthoceras