Eckhardite is a very rare secondary tellurium mineral primarily found at the Moctezuma mine in Mexico. It typically forms small, yellow, tabular crystals or crusts within the oxidized zones of hydrothermal deposits associated with other rare tellurites.
Is this eckhardite?
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 eckhardite with a known reference. Eckhardite sits at Mohs 2-3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: very pale bluish green.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to subadamantine.
- 4Match the color rangeCompare against the expected color range: yellow, yellow-green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular to blocky crystals, often as crusts or aggregates.
Often confused with
Eckhardite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Eckhardite leaves very pale bluish green, Cesbronite leaves pale green; luster reads vitreous to subadamantine on Eckhardite and subadamantine on Cesbronite.
How to tell apart: Streak differs, so Eckhardite leaves very pale bluish green, Quetzalcoatlite leaves pale blue, almost white; luster reads vitreous to subadamantine on Eckhardite and pearly to dull on Quetzalcoatlite.
Often found alongside eckhardite
Minerals reported to co-occur with eckhardite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaCuTeO₅(H₂O)
- Mohs hardness
- 2-3
- Density
- 4.644 g/cm³
- Colors
- Streak
- Very pale bluish green
- Luster
- Vitreous to subadamantine
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular to blocky crystals, often as crusts or aggregates
- Cleavage
- Likely but not observed on {101}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral in vugs in quartz formed from the partial oxidation of primary sulfides and tellurides during or following the brecciation of quartz veins
Where rockhounds find eckhardite
Classic worldwide localities
- Bird Nest drift and Aga mine, Otto Mountain, near Baker, San Bernardino County, California, USA
Field-hunting tip
Where it forms: A secondary mineral in vugs in quartz formed from the partial oxidation of primary sulfides and tellurides during or following the brecciation of quartz veins. If you start seeing br-rich chlorargyrite, gold, housleyite in float, you are in the right ground. Typical habit: tabular to blocky crystals, often as crusts or aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
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Find eckhardite on the map
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