Mackayite is a rare iron tellurite mineral typically found in the oxidation zones of tellurium-rich hydrothermal deposits. It most commonly appears as small, dark green to yellowish-green tabular crystals or granular crusts associated with other secondary tellurium minerals.
Is this mackayite?
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 mackayite with a known reference. Mackayite 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. Mackayite leaves a yellowish streak.
- 3Read the lusterHold the specimen under a strong light. Mackayite typically shows a sub-adamantine luster.
- 4Match the color rangeCompare against the expected color range: dark green, yellowish-green, brownish-green.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: tabular crystals, granular aggregates.
Often confused with
Mackayite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Mackayite leaves yellowish, Emmonsite leaves pale yellow; luster reads sub-adamantine on Mackayite and vitreous on Emmonsite.
How to tell apart: Streak differs — Mackayite leaves yellowish, Rodalquilarite leaves pale yellow; luster reads sub-adamantine on Mackayite and adamantine on Rodalquilarite.
Often found alongside mackayite
Minerals reported to co-occur with mackayite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe³⁺Te₂O₅(OH)
- Mohs hardness
- 4.5
- Density
- 5.5 g/cm³
- Streak
- Yellowish
- Luster
- Sub-adamantine
- Transparency
- Translucent
- Crystal system
- Tetragonal
- Crystal habit
- Tabular Crystals, Granular Aggregates
- Cleavage
- None Observed
- Rarity
- Rare
- Uses
- Collector, Scientific Research
- Host rock
- Oxidized Tellurium-bearing Hydrothermal Veins
- Typical price
- $50-300 for small thumbnail specimens
Where rockhounds find mackayite
Classic worldwide localities
- Bisbee, Arizona (USA)
- Goldfield, Nevada (USA)
- Moctezuma, Sonora (Mexico)
Field-hunting tip
Look in oxidized tellurium-bearing hydrothermal veins country — that is the host setting where mackayite typically forms. If you start seeing emmonsite, tellurite, quartz in float, you are in the right ground. Field specimens usually show a tabular crystals, granular aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find mackayite on the map
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