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.
Is this guanine?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch guanine with a known reference. Guanine sits at Mohs 1-2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: pearly.
- 4Match the color rangeCompare against the expected color range: white.
- 5Look at form & habitCrystal system: monoclinic. 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.
All properties
- Chemical formula
- C₅H₅N₅O
- Mohs hardness
- 1-2
- Density
- 1.485 g/cm³
- Colors
- Streak
- White
- Luster
- Pearly
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Platy or needle-like crystals
- Cleavage
- None
- Rarity
- Common
- Uses
- Biological research, Collector
- Host rock
- An uncommon component of phosphatic crusts associated with guano from seabirds or bats
Where rockhounds find guanine
Classic worldwide localities
- North Chincha Island, off the coast of Peru
- Murra-el-elevyn Cave, Cocklebiddy, and Petrogale Cave, near Madura, Western Australia
Field-hunting tip
Where it forms: An uncommon component of phosphatic crusts associated with guano from seabirds or bats. If you start seeing aphthitalite, biphosphammite, brushite in float, you are in the right ground. Typical habit: platy or needle-like crystals. Train your eye for that shape before scanning the outcrop.
Common questions
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Find guanine on the map
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