Specimen at a glance
| Mineral | Calcite |
|---|---|
| Chemistry | CaCO3 |
| Mohs hardness | 3 |
| Crystal system | Trigonal |
| Locality | Ilion Gorge, New York |
| Form | Raw / rough |
| You receive | The exact specimen pictured |
About this specimen
Travertine is a form of calcite (calcium carbonate) deposited by flowing or seeping mineral-rich water, building up in layers over time much the way stalactites and stalagmites form in caves — except here as banded crusts and botryoidal (grape-like) growths on exposed rock rather than inside a cave chamber. It’s classified as a “secondary” mineral formation, meaning it forms from water depositing new material onto existing rock, rather than crystallizing directly within a sealed cavity the way many display-quality mineral specimens do.
This specimen comes from Ilion Gorge in Herkimer County, New York, a locality documented by mineral collectors for its travertine deposits, and shows warm tan botryoidal calcite growth layered over banded travertine with delicate sprays of white calcite. At Mohs hardness 3, it’s soft and should be handled gently, cleaned with just a soft, dry cloth.
Approximately 3.5 x 2.5″, it’s a great example of secondary mineral formation in action and a nice regional locality piece for New York mineral collectors or anyone interested in how water shapes rock over time.
Inside the Calcite
One of the most common minerals on Earth — and one of the only ones you can prove is calcite with nothing but a coin and a drop of vinegar.
The story: Calcite crystallizes out of calcium-rich water almost anywhere conditions allow — caves, hydrothermal veins, sedimentary pockets — which is why it shows up in more shapes than almost any other mineral: sharp dogtooth points, flat nailhead rhombs, honey-gold masses, even the travertine that lines old hot springs. Every one of those forms is chemically the same mineral, just grown under different conditions.
Why collectors chase it: Calcite is the classic demonstration of birefringence — a clear piece laid over printed text splits the letters into a visible double image, a party trick that only a handful of minerals can do. Add in the sheer range of natural color and habit (the golden-toned Ohio pieces get their warmth from iron staining) and it’s an easy mineral to build a whole sub-collection around.
Care: This is the one to handle more carefully than most of the shop: at Mohs 3 it scratches under a fingernail-plus-effort, it splits cleanly along three flat planes if dropped (perfect rhombohedral cleavage), and it will visibly fizz on contact with vinegar or other mild acids — keep it away from acidic cleaners and store it apart from harder stones that could scratch it.
Calcite: the science
- Calcite has perfect rhombohedral cleavage: tap it hard and it breaks into slanted blocks along three directions.
- Clear calcite shows double refraction. Set it on printed text and you see the letters twice.
- It fizzes in weak acid, a classic field test. That is also why acid cleaners will damage it.
Go deeper
Want the full story on calcite: how it forms, how to identify it, and what makes a great specimen?
Questions about this piece
What is calcite?
Calcite is calcium carbonate, the mineral that makes up limestone, marble, cave formations, and many seashells. It crystallizes in more shapes than almost any other mineral.
Where was it found?
This piece comes from Ilion Gorge, New York. We list a locality whenever it is known, because where a mineral formed is part of its story and its value.
How hard is it, and how should I care for it?
It rates 3 on the Mohs scale. Calcite is soft (Mohs 3) and cleaves easily. Handle gently, never use vinegar or acid cleaners, and dust with a soft brush. Rinse only briefly in plain water.
Is this the exact piece I will receive?
Yes. This listing was photographed individually, and you receive the exact piece shown in the photos.
