Ankerite is a common member of the dolomite group that often displays characteristic brownish or yellowish staining due to iron oxidation. It typically forms sharp rhombohedral crystals and is frequently found in hydrothermal vein deposits alongside other carbonates and sulfide minerals.
Is this ankerite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch ankerite with a known reference. Ankerite sits at Mohs 3.5-4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to pearly.
- 4Match the color rangeCompare against the expected color range: white, yellow, brown, gray, brownish yellow, gray, gray brown.
- 5Look at form & habitCrystal system: trigonal. Typical habit: crystalline, granular, massive.
Often confused with
Ankerite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside ankerite
Minerals reported to co-occur with ankerite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaFe(CO₃)₂
- Mohs hardness
- 3.5-4
- Density
- 2.93-3.10 g/cm³
- Streak
- White
- Luster
- Vitreous to pearly
- Transparency
- Translucent to transparent
- Crystal system
- Trigonal
- Crystal habit
- Crystalline, granular, massive
- Cleavage
- On {1011}, perfect
- Rarity
- Common
- Uses
- Collector, Geological specimen
- Host rock
- Formed in low-grade metamorphosed ironstones and sedimentary banded iron formations; in carbonatites
Where rockhounds find ankerite
5 mapped spotsClassic worldwide localities
- Roxbury iron mine, Litchfield Co., Connecticut, USA
- Jeffrey quarry, near Little Rock, Pulaski Co., Arkansas, USA
- Eagle mine, Gilman district, Eagle Co., Colorado, USA
- Mesabi Range, Minnesota, USA
- Styria, from the Erzberg, Eisenerz, and at Gollrad, Austria
- Steiermark, Austria
Field-hunting tip
Where it forms: Formed in low-grade metamorphosed ironstones and sedimentary banded iron formations; in carbonatites. If you start seeing siderite, dolomite in float, you are in the right ground. Typical habit: crystalline, granular, massive. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Colorado, Massachusetts, North Carolina. Start trip planning there.
Common questions
How do you identify ankerite?+
Where is ankerite found?+
Can I find ankerite in the United States?+
What rocks look like ankerite?+
What minerals are found with ankerite?+
What kind of rock does ankerite form in?+
What is ankerite used for?+
Find ankerite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
