Ternesite is a rare calcium silicate sulfate mineral typically found in combustion metamorphic settings or within high-temperature industrial slags. It usually occurs as small, colorless to pale yellow prismatic crystals that can be difficult to distinguish from common sulfates without chemical testing.
Is this ternesite?
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 ternesite with a known reference. Ternesite sits at Mohs 4.5, 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.
- 4Match the color rangeCompare against the expected color range: colorless, bright blue.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: aggregates, radial.
Often confused with
Ternesite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside ternesite
Minerals reported to co-occur with ternesite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₅(SiO₄)₂(SO₄)
- Mohs hardness
- 4.5
- Density
- 2.94-2.98 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Aggregates, radial
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- In calcium-rich xenoliths in leucite tephrite lava
Where rockhounds find ternesite
Classic worldwide localities
- The Ettringer Bellerberg, near Mayen, Eifel, Germany (type locality)
Field-hunting tip
Where it forms: In calcium-rich xenoliths in leucite tephrite lava. If you start seeing ettringite, portlandite, afwillite in float, you are in the right ground. Typical habit: aggregates, radial. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ternesite?+
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What rocks look like ternesite?+
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Find ternesite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
