Tertschite is a rare hydrated calcium borate mineral that typically forms as delicate, needle-like acicular crystals or white powdery efflorescences. It is primarily found in association with other borate minerals in sedimentary evaporite deposits, most notably in Turkey. Collectors should handle these specimens with care due to their fragility and tendency to dehydrate in low-humidity environments.
Is this tertschite?
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 tertschite with a known reference. Tertschite sits at Mohs 2, 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: silky.
- 4Match the color rangeCompare against the expected color range: snow white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: fibrous.
Often confused with
Tertschite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads silky on Tertschite and vitreous; silky or satiny in fibrous aggregates on Ulexite.
How to tell apart: Colemanite is the harder of the two (Mohs 4.5 vs. 2); luster reads silky on Tertschite and vitreous to adamantine on Colemanite.
Often found alongside tertschite
Minerals reported to co-occur with tertschite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₄B₁₀O₁₉·20H₂O
- Mohs hardness
- 2
- Density
- 1.97 g/cm³
- Colors
- Streak
- White
- Luster
- Silky
- Transparency
- Semitransparent
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous
- Cleavage
- None
- Fluorescence
- Blue violet under SW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In a borate deposit
Where rockhounds find tertschite
Classic worldwide localities
- Kurtpınarımine, near Faras, Bigadiç borate district, Balıkesir Province, Turkey
Field-hunting tip
Where it forms: In a borate deposit. If you start seeing colemanite, meyerhofferite, ulexite in float, you are in the right ground. Typical habit: fibrous. Train your eye for that shape before scanning the outcrop.
Common questions
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Find tertschite on the map
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