Nobleite is a rare calcium borate mineral that typically forms as small, clear, tabular crystals or delicate crusts in arid borate evaporite deposits. Collectors value it for its sharp, glassy crystal habit, though it is usually found in very limited quantities in its type locality in Death Valley.
Is this nobleite?
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 nobleite with a known reference. Nobleite 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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: subvitreous, pearly on cleavages.
- 4Match the color rangeCompare against the expected color range: colorless, white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals, radiating aggregates, crusts.
Often confused with
Nobleite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Colemanite is the harder of the two (Mohs 4.5 vs. ~3); luster reads subvitreous, pearly on cleavages on Nobleite and vitreous to adamantine on Colemanite.
How to tell apart: Luster reads subvitreous, pearly on cleavages on Nobleite and vitreous; silky or satiny in fibrous aggregates on Ulexite.
How to tell apart: Nobleite is noticeably harder (Mohs ~3 vs. 2); luster reads subvitreous, pearly on cleavages on Nobleite and vitreous on Inyoite.
Often found alongside nobleite
Minerals reported to co-occur with nobleite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaB₆O₉(OH)₂·3H₂O
- Mohs hardness
- ~3
- Density
- 2.09 g/cm³
- Streak
- White
- Luster
- Subvitreous, pearly on cleavages
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular crystals, radiating aggregates, crusts
- Cleavage
- Perfect on {100}; indistinct on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Typically a recent incrustation produced by weathering of colemanite and priceite veins in altered olivine basalt and basaltic clastic rocks (near the De Bely mine, California, USA)
Where rockhounds find nobleite
Classic worldwide localities
- Furnace Creek district, Death Valley, Inyo Co., California, from one km north-northwest of the De Bely mine, USA
- Coarsely crystalline in the Corkscrew mine, California, USA
- Sijes district, Salta Province, Argentina
- Drill core at Piskanja, Jarandol basin, Serbia
Field-hunting tip
Where it forms: Typically a recent incrustation produced by weathering of colemanite and priceite veins in altered olivine basalt and basaltic clastic rocks (near the De Bely mine, California, USA). If you start seeing colemanite, meyerhofferite, gowerite in float, you are in the right ground. Typical habit: tabular crystals, radiating aggregates, crusts. Train your eye for that shape before scanning the outcrop.
Common questions
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Find nobleite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
