Archerite is a rare phosphate mineral formed in cave environments where guano reacts with silicate minerals. It is typically found as fragile, colorless crystalline crusts and is highly soluble in water, requiring careful storage in a dry environment.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Translucent

mineralrare

Archerite

Hardness: 2
Luster: Vitreous
Streak: White
Transparency: Translucent

Is this archerite?

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 archerite with a known reference. Archerite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: 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: beige, white.
5
Look at form & habit
Crystal system: tetragonal. Typical habit: small crystalline crusts and aggregates.

Often confused with

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

mineral

Biphosphammite

Mohs 1-2

How to tell apart: Luster reads vitreous on Archerite and dull, earthy; crystals rarely vitreous on Biphosphammite.

Often found alongside archerite

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

All properties

Chemical formula: H₂KPO₄
Mohs hardness: 2
Density: 2.23 g/cm³
Colors: Beige White
Streak: White
Luster: Vitreous
Transparency: Translucent
Crystal system: Tetragonal
Crystal habit: Small crystalline crusts and aggregates
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: As a component of ~talactites and crusts on the walls of caves containing bat guano deposits

Where rockhounds find archerite

Classic worldwide localities

Petrogale Cave, near Madura, and in Murra-el-elevyn Cave, about 200 km east of Balladonia, Western Australia

Field-hunting tip

Where it forms: As a component of ~talactites and crusts on the walls of caves containing bat guano deposits. If you start seeing biphosphammite, aphthitalite, halite in float, you are in the right ground. Typical habit: small crystalline crusts and aggregates. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify archerite?+

Mohs hardness is 2. Luster: vitreous. The streak is white. Common colors include beige, white.

Where is archerite found?+

Notable localities include Petrogale Cave, near Madura, and in Murra-el-elevyn Cave, about 200 km east of Balladonia, Western Australia.

What rocks look like archerite?+

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

What minerals are found with archerite?+

Archerite commonly co-occurs with Biphosphammite, Aphthitalite, Halite, Syngenite, Stercorite, Oxammite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does archerite form in?+

Where it forms: As a component of ~talactites and crusts on the walls of caves containing bat guano deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is archerite used for?+

Archerite is used in collector.

Find archerite on the map

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