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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.

Hardness
4.5
Mohs
Luster
Vitreous
Streak
Pale green
Transparency
Transparent

Is this mackayite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

  • 1
    Test the hardness
    Try to scratch mackayite with a known reference. Mackayite sits at Mohs 4.5, softer than the next harder reference, harder than the previous one.
  • 2
    Check the streak
    Drag the specimen across an unglazed porcelain plate. Streak: pale green.
  • 3
    Read the luster
    Hold the specimen under a strong light. Luster: vitreous.
  • 4
    Match the color range
    Compare against the expected color range: brownish green, yellow green, olive green.
  • 5
    Look at form & habit
    Crystal 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.

Emmonsite mineral
mineral
Emmonsite
Mohs ~5
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Rodalquilarite mineral
mineral
Rodalquilarite
Mohs 2-3

How to tell apart: Mackayite is noticeably harder (Mohs 4.5 vs. 2-3); streak differs, so Mackayite leaves pale green, Rodalquilarite leaves greenish yellow; luster reads vitreous on Mackayite and greasy on Rodalquilarite.

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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
4.86 g/cm³
Colors
Brownish greenYellow greenOlive green
Streak
Pale green
Luster
Vitreous
Transparency
Transparent
Crystal system
Tetragonal
Crystal habit
Tabular crystals, granular aggregates
Cleavage
None
Rarity
Rare
Uses
Collector, Scientific research
Host rock
Of rare occurrence in the oxidized zone of Au–Te deposits, an alteration product of tellurium

Where rockhounds find mackayite

Classic worldwide localities

  • Mohawk mine, and between the Jumbo and Clermont mines, Goldfield, Esmeralda Co., Nevada, USA
  • Toughnut-Empire mine, Tombstone, Cochise Co., Arizona, USA
  • A prospect near the Lone Pine mine, Wilcox district, Catron Co., New Mexico, USA
  • Klondike mine, Saguache Co., Colorado, USA
  • Moctezuma (Bambolla) mine and the San Miguel and La Candelaria prospects, south of Moctezuma, and from Onovas, Sonora, Mexico
  • El Indio mine, El Indio-Tambo district, east of La Serena, Coquimbo, Chile

Field-hunting tip

Where it forms: Of rare occurrence in the oxidized zone of Au–Te deposits, an alteration product of tellurium. If you start seeing tellurium, tellurite, emmonsite in float, you are in the right ground. Typical habit: tabular crystals, granular aggregates. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify mackayite?+
Mohs hardness is 4.5. Luster: vitreous. The streak is pale green. Common colors include brownish green, yellow green, olive green.
Where is mackayite found?+
Notable localities include Mohawk mine, and between the Jumbo and Clermont mines, Goldfield, Esmeralda Co., Nevada, USA; Toughnut-Empire mine, Tombstone, Cochise Co., Arizona, USA; A prospect near the Lone Pine mine, Wilcox district, Catron Co., New Mexico, USA; Klondike mine, Saguache Co., Colorado, USA; Moctezuma (Bambolla) mine and the San Miguel and La Candelaria prospects, south of Moctezuma, and from Onovas, Sonora, Mexico.
Is mackayite safe to handle?+
Contains tellurium and iron; wash hands thoroughly after handling and avoid inhaling dust.
What rocks look like mackayite?+
Mackayite is most often confused with Emmonsite, Rodalquilarite. A quick hardness test and a streak check separate the look-alikes faster than color alone.
What minerals are found with mackayite?+
Mackayite commonly co-occurs with Tellurium, Tellurite, Emmonsite, Rodalquilarite, Poughite, Cliffordite. Spotting any of these in float or country rock is a useful trip signal.
What kind of rock does mackayite form in?+
Where it forms: Of rare occurrence in the oxidized zone of Au–Te deposits, an alteration product of tellurium. Working float back to the host body is the standard way to chase a fresh occurrence.
What is mackayite used for?+
Mackayite is used in collector, scientific research.

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