Fairchildite is a rare potassium calcium carbonate mineral typically found in environments associated with burning coal seams or volcanic vents. It is extremely unstable in moist air, often dehydrating or altering rapidly, making it a challenging and prized specimen for serious mineral collectors.
Is this fairchildite?
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 fairchildite with a known reference. Fairchildite sits at Mohs 3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Fairchildite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Fairchildite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, gray.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: platy crystals, crusts, or coatings.
Often confused with
Fairchildite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside fairchildite
Minerals reported to co-occur with fairchildite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K₂Ca(CO₃)₂
- Mohs hardness
- 3
- Density
- 2.44 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Hexagonal
- Crystal habit
- Platy Crystals, Crusts, Or Coatings
- Cleavage
- Good
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Burning Coal Seams, Volcanic Vents
- Typical price
- $50-300 per specimen
Where rockhounds find fairchildite
Classic worldwide localities
- Old Faithful, Yellowstone National Park, USA
- Centralia coal mine, Pennsylvania, USA
Field-hunting tip
Look in burning coal seams, volcanic vents country — that is the host setting where fairchildite typically forms. If you start seeing bucanite, calcite, aragonite in float, you are in the right ground. Field specimens usually show a platy crystals, crusts, or coatings habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify fairchildite?+
Where is fairchildite found?+
How much is fairchildite worth?+
What rocks look like fairchildite?+
What minerals are found with fairchildite?+
What kind of rock does fairchildite form in?+
What is fairchildite used for?+
Find fairchildite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
