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Ankerite
Ankerite is carbonate (dolomite group), Ca(Fe,Mg)(CO₃)₂. In the hand, it rates 3.5 to 4 on the Mohs scale, and it runs cream to tan fresh and brown to rusty when weathered. Dolomite's iron-rich cousin, cream saddle-shaped rhombs that weather to telltale rusty brown and fizz only weakly in cold vinegar.
The geology.
Ankerite carries the formula Ca(Fe,Mg)(CO₃)₂. It belongs to the trigonal system. Its listing category is carbonate (dolomite group).
It sits at 3.5 to 4 on the Mohs scale. The surface reads vitreous to pearly. Light behaviour is translucent to opaque. Specific gravity runs 2.9 to 3.1. The streak is white. It breaks with perfect rhombohedral cleavage.
Dolomite's iron-rich cousin, cream saddle-shaped rhombs that weather to telltale rusty brown and fizz only weakly in cold vinegar.
It turns up mostly as curved saddle rhombs, vein fillings with quartz and gold or massive.
The origins.
Hydrothermal veins and iron formations; classic companion of gold-quartz veins worldwide (Australia, Canada, California).
On value, the database notes: inexpensive; mainly field-collector interest.
Traditional associations.
In energy work traditions, ankerite has little established lore; it is occasionally sold under generic 'brown calcite' grounding themes.
This is lore, and we label it as lore. The measurable facts are further up the page.
Spotting the real thing.
Dolomite's iron-rich cousin, cream saddle-shaped rhombs that weather to telltale rusty brown and fizz only weakly in cold vinegar.
| Looks like | How to tell them apart |
|---|---|
| Dolomite | Essentially identical fresh; ankerite turns rusty brown on weathered surfaces (iron) |
| Siderite | Siderite is denser, browner throughout, and fizzes only in warm acid |
| Calcite | Calcite fizzes vigorously cold; ankerite barely reacts unless powdered |
At-home tests.
A loupe and a window seat settle most questions about ankerite. No workshop required.
| Test | What you should see |
|---|---|
| Acid check | Weak fizz cold, stronger warm or powdered |
| By eye | Rusty weathering rims |
| By eye | Curved rhombohedral crystals |
Anything that scratches, burns or dissolves the piece is a lab job. Get it appraised rather than testing it apart.
Care & handling.
At 3.5 to 4 on the Mohs scale this is a soft material. Keep it as a display piece, store it apart from harder stones, and skip daily-wear settings.
It breaks with perfect rhombohedral cleavage, which is worth knowing before you set it or drop it.
Warm water and a soft cloth clean almost everything. Ultrasonic tanks, steamers and household cleaners are where pieces get ruined.
A deeper look.
Extended detail on composition, sourcing, authentication and market value.
The physical record
The formula on record is Ca(Fe,Mg)(CO₃)₂. Crystal system: Trigonal. Specific gravity: 2.9 to 3.1. Streak: White. Cleavage and fracture: Perfect rhombohedral cleavage.
How it reaches the market
Hydrothermal veins and iron formations; classic companion of gold-quartz veins worldwide (Australia, Canada, California).
What it gets confused with
Dolomite: Essentially identical fresh; ankerite turns rusty brown on weathered surfaces (iron). Siderite: Siderite is denser, browner throughout, and fizzes only in warm acid. Calcite: Calcite fizzes vigorously cold; ankerite barely reacts unless powdered.
What it is worth
Inexpensive; mainly field-collector interest.
One more thing
Old-time gold prospectors watched for rusty ankerite veins, the carbonate often rides shotgun with gold-bearing quartz.
An education-first guide.
No product links here. We do not sell ankerite, and a guide that only covers our own shelves would not be much of a guide.
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