Cuprorivaite is a rare calcium copper silicate known historically as the main component of the synthetic pigment Egyptian Blue. In nature, it occurs as small, vibrant blue platy crystals in thermally metamorphosed limestone blocks found in volcanic ejecta.
Is this cuprorivaite?
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 cuprorivaite with a known reference. Cuprorivaite sits at Mohs ~5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: light blue.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: blue.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: tabular.
Often confused with
Cuprorivaite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Cuprorivaite is noticeably harder (Mohs ~5 vs. 3.5-4); streak differs, so Cuprorivaite leaves light blue, Azurite leaves pale blue.
How to tell apart: Streak differs, so Cuprorivaite leaves light blue, Turquoise leaves white to pale greenish blue.
Often found alongside cuprorivaite
Minerals reported to co-occur with cuprorivaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaCuSi₄O₁₀
- Mohs hardness
- ~5
- Density
- 3.08 g/cm³
- Colors
- Streak
- Light blue
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Tetragonal
- Crystal habit
- Tabular
- Cleavage
- Perfect on {001}
- Rarity
- Rare
- Uses
- Collector, Pigment (historical)
- Host rock
- Intimately mixed with quartz (Vesuvius, Italy); in a mudstone xenolith ejected from a scoria cone (Sattelberg volcanic cone, Germany)
Where rockhounds find cuprorivaite
Classic worldwide localities
- Summit Rock, near Diamond Lake, Douglas Co., Oregon, USA
- Vesuvius, Campania, Italy
- Wheal Edward, Cornwall, England
- Sattelberg volcanic cone, near Brenk, Eifel district, Germany
- Messina, Transvaal, South Africa
Field-hunting tip
Where it forms: Intimately mixed with quartz (Vesuvius, Italy); in a mudstone xenolith ejected from a scoria cone (Sattelberg volcanic cone, Germany). If you start seeing quartz in float, you are in the right ground. Typical habit: tabular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify cuprorivaite?+
Where is cuprorivaite found?+
Is cuprorivaite safe to handle?+
What rocks look like cuprorivaite?+
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Find cuprorivaite on the map
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