Keystoneite is a rare magnesium nickel iron oxide, typically golden yellow. It was approved as a distinct mineral species in 1987. It was first described from Keystone mine, Magnolia district, Boulder Co., Colorado, USA.

Hardness

2-3

Mohs

Luster

Adamantine

Streak

Pale yellow-green

Transparency

Semitransparent

mineralrareChalcomenite Group family

Keystoneite

Hardness: 2-3
Luster: Adamantine
Streak: Pale yellow-green
Transparency: Semitransparent

No image

Is this keystoneite?

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 keystoneite with a known reference. Keystoneite sits at Mohs 2-3, 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 yellow-green.
3
Read the luster
Hold the specimen under a strong light. Luster: adamantine.
4
Match the color range
Compare against the expected color range: golden yellow, orange yellow.
5
Look at form & habit
Crystal system: hexagonal. Typical habit: acicular, radial.

Often confused with

Keystoneite vs. its common look-alikes, and how to tell them apart in the field.

mineral

Chalcomenite

Mohs 2-2.5

How to tell apart: Streak differs, so Keystoneite leaves pale yellow-green, Chalcomenite leaves light blue; luster reads adamantine on Keystoneite and vitreous on Chalcomenite.

Often found alongside keystoneite

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

All properties

Chemical formula: Mg₀.₅NiFe³⁺(Te⁴⁺O₃)₃·4H₂O
Mohs hardness: 2-3
Density: 4.4 g/cm³
Colors: Golden yellow Orange yellow
Streak: Pale yellow-green
Luster: Adamantine
Transparency: Semitransparent
Crystal system: Hexagonal
Crystal habit: Acicular, radial
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: A rare secondary mineral formed in the oxidized zone of a complex polymetallic hydrothermal mineral deposit

Where rockhounds find keystoneite

Classic worldwide localities

Keystone mine, Magnolia district, Boulder Co., Colorado, USA

Field-hunting tip

Where it forms: A rare secondary mineral formed in the oxidized zone of a complex polymetallic hydrothermal mineral deposit. If you start seeing melonite, tellurium, paratellurite in float, you are in the right ground. Typical habit: acicular, radial. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify keystoneite?+

Mohs hardness is 2-3. Luster: adamantine. The streak is pale yellow-green. Common colors include golden yellow, orange yellow.

Where is keystoneite found?+

Notable localities include Keystone mine, Magnolia district, Boulder Co., Colorado, USA.

Is keystoneite safe to handle?+

Keystoneite contains nickel. Contains nickel and tellurium, which are toxic if ingested or inhaled as dust. Wash hands thoroughly after handling and avoid creating dust.

What rocks look like keystoneite?+

Keystoneite is most often confused with Chalcomenite, Malachite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with keystoneite?+

Keystoneite commonly co-occurs with Melonite, Tellurium, Paratellurite, Magnolite, Coloradoite, Calaverite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does keystoneite form in?+

Where it forms: A rare secondary mineral formed in the oxidized zone of a complex polymetallic hydrothermal mineral deposit. Working float back to the host body is the standard way to chase a fresh occurrence.

What is keystoneite used for?+

Keystoneite is used in collector.

Find keystoneite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.