Guanine is a naturally occurring organic base derived from the accumulation of bird or bat guano, often found as a white, chalky material. It is a biological mineral species that crystallizes in evaporite environments associated with massive avian waste deposits.

Hardness

1.5-2

Mohs

Luster

Pearly

Streak

White

Transparency

Opaque

fossilcommon

Guanine

Hardness: 1.5-2
Luster: Pearly
Streak: White
Transparency: Opaque

Is this guanine?

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 guanine with a known reference. Guanine sits at Mohs 1.5-2 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Guanine leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Guanine typically shows a pearly luster.
4
Match the color range
Compare against the expected color range: white, colorless.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: platy or needle-like crystals.

Often found alongside guanine

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

Aphthitalite
mineral · Mohs 3-3.5

All properties

Chemical formula: C₅H₅N₅O
Mohs hardness: 1.5-2
Density: 1.58 g/cm³
Colors: White Colorless
Streak: White
Luster: Pearly
Transparency: Opaque
Crystal system: Orthorhombic
Crystal habit: Platy or Needle-like Crystals
Cleavage: None
Rarity: Common
Uses: Biological Research, Collector
Host rock: Guano Deposits
Typical price: $10-50 per small sample

Where rockhounds find guanine

Classic worldwide localities

Peru
Chile
Nauru
Christmas Island

Field-hunting tip

Look in guano deposits country — that is the host setting where guanine typically forms. If you start seeing uric acid, aphthitalite in float, you are in the right ground. Field specimens usually show a platy or needle-like crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify guanine?+

Mohs hardness is 1.5-2. It typically shows a pearly luster. The streak is white. Common colors include white, colorless.

Where is guanine found?+

Notable localities include Peru; Chile; Nauru; Christmas Island.

How much is guanine worth?+

Typical asking prices fall in the range of $10-50 per small sample. Quality, size, and provenance can move individual specimens well outside that range.

What minerals are found with guanine?+

Guanine commonly co-occurs with Uric Acid, Aphthitalite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does guanine form in?+

Guanine typically forms in guano deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is guanine used for?+

Guanine is used in biological research, collector.

Find guanine on the map

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