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

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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, 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.