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Agardite-(La) is a rare secondary copper arsenate mineral found in the oxidation zones of ore deposits. It is best identified by its vibrant green or yellow-green color and characteristic radiating sprays of tiny, needle-like acicular crystals.

Hardness
3-4
Mohs
Luster
Vitreous
Streak
Greenish white
Transparency
Semitransparent

Is this agardite-(la)?

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 agardite-(la) with a known reference. Agardite-(La) sits at Mohs 3-4, softer than the next harder reference, harder than the previous one.
  • 2
    Check the streak
    Drag the specimen across an unglazed porcelain plate. Streak: greenish white.
  • 3
    Read the luster
    Hold the specimen under a strong light. Luster: vitreous.
  • 4
    Match the color range
    Compare against the expected color range: colorless, yellowish green, blue.
  • 5
    Look at form & habit
    Crystal system: hexagonal. Typical habit: acicular.

Often confused with

Agardite-(La) vs. its common look-alikes, and how to tell them apart in the field.

Mixite mineral
mineral
Mixite
Mohs 3-4

How to tell apart: Streak differs, so Agardite-(La) leaves greenish white, Mixite leaves pale bluish green.

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Austinite mineral
mineral
Austinite
Mohs 4-4.5

How to tell apart: Streak differs, so Agardite-(La) leaves greenish white, Austinite leaves white; luster reads vitreous on Agardite-(La) and subadamantine to silky in aggregates on Austinite.

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Often found alongside agardite-(la)

Minerals reported to co-occur with agardite-(la). Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula
Cu₆La(AsO₄)₃(OH)₆·3H₂O
Mohs hardness
3-4
Density
3.65 g/cm³
Colors
ColorlessYellowish greenBlue
Streak
Greenish white
Luster
Vitreous
Transparency
Semitransparent
Crystal system
Hexagonal
Crystal habit
Acicular
Cleavage
None
Rarity
Rare
Uses
Collector, Mineralogical research
Host rock
In small amounts in the oxidized zone of hydrothermal mineralized breccia and polymetallic mineral deposits (Red Cloud mines, New Mexico, USA)

Where rockhounds find agardite-(la)

Classic worldwide localities

  • Red Cloud fluorite and copper mines, Gallinas district, Lincoln Co., New Mexico, USA
  • Kamariza mine, Laurium, Greece (Ce > La in part)
  • Wheal Alfred, Phillack, Cornwall (Nd-rich), England
  • Brandy Gill and Deer Hills mines, Caldbeck Fells, Cumbria, England
  • Clara Mine, near Oberwolfach, and other localities in the Black Forest, Germany (Ce > La in part)
  • Sa Duchessa mine, near Iglesias, Sardinia, Italy (Nd-part, some with Ce > La)

Field-hunting tip

Where it forms: In small amounts in the oxidized zone of hydrothermal mineralized breccia and polymetallic mineral deposits (Red Cloud mines, New Mexico, USA). If you start seeing fluorite, bastnaesite, barite in float, you are in the right ground. Typical habit: acicular. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify agardite-(la)?+
Mohs hardness is 3-4. Luster: vitreous. The streak is greenish white. Common colors include colorless, yellowish green, blue.
Where is agardite-(la) found?+
Notable localities include Red Cloud fluorite and copper mines, Gallinas district, Lincoln Co., New Mexico, USA; Kamariza mine, Laurium, Greece (Ce > La in part); Wheal Alfred, Phillack, Cornwall (Nd-rich), England; Brandy Gill and Deer Hills mines, Caldbeck Fells, Cumbria, England; Clara Mine, near Oberwolfach, and other localities in the Black Forest, Germany (Ce > La in part).
Is agardite-(la) safe to handle?+
Agardite-(La) contains arsenic and copper and calls for real care. Contains arsenic. Wash hands thoroughly after handling and avoid inhaling dust.
What rocks look like agardite-(la)?+
Agardite-(La) is most often confused with Mixite, Austinite. A quick hardness test and a streak check separate the look-alikes faster than color alone.
What minerals are found with agardite-(la)?+
Agardite-(La) commonly co-occurs with Fluorite, Bastnaesite, Barite, Quartz, Chrysocolla, Malachite. Spotting any of these in float or country rock is a useful trip signal.
What kind of rock does agardite-(la) form in?+
Where it forms: In small amounts in the oxidized zone of hydrothermal mineralized breccia and polymetallic mineral deposits (Red Cloud mines, New Mexico, USA). Working float back to the host body is the standard way to chase a fresh occurrence.
What is agardite-(la) used for?+
Agardite-(La) is used in collector, mineralogical research.

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