Phosphorite is a sedimentary rock that contains a high concentration of phosphate minerals, typically apatite group members. It is often found as nodular or massive beds in marine environments and is the primary source of phosphorus for industrial fertilizer production. Collectors prize these for their often-biogenic origin, as they frequently contain fossilized bone fragments or shark teeth.
Is this phosphorite?
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 phosphorite with a known reference. Phosphorite sits at Mohs 3-5, softer than the next harder reference, harder than the previous one.
- 2Read the textureLook at a fresh break with a hand lens. Texture: Cryptocrystalline masses (collophane). Grain size: Under 1 micrometre.
- 3Pick out the mineralsComposition: Phosphate minerals, mainly fluorapatite; 4 to 20 percent phosphorus pentoxide. Identify the two or three most abundant grains.
- 4Read the lusterHold the specimen under a strong light. Luster: dull.
- 5Match the color rangeCompare against the expected color range: gray, brown, black, white, yellow.
Often confused with
Phosphorite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Chert is the harder of the two (Mohs 6.5-7 vs. 3-5); luster reads dull on Phosphorite and waxy on Chert.
How to tell apart: Luster reads dull on Phosphorite and vitreous to pearly on Dolomite.
Often found alongside phosphorite
Minerals reported to co-occur with phosphorite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 3-5
- Density
- 2.0-3.0 g/cm³
- Luster
- Dull
- Transparency
- Opaque
- Rarity
- Common
- Uses
- Industrial, Agricultural, Collector
- Host rock
- sedimentary deposits
- Texture
- Cryptocrystalline masses (collophane)
- Grain size
- Under 1 micrometre
- Composition
- Phosphate minerals, mainly fluorapatite; 4 to 20 percent phosphorus pentoxide
Where rockhounds find phosphorite
6 mapped spotsClassic worldwide localities
- Florida, USA
- North Carolina, USA
- Morocco
- China
- Russia
Field-hunting tip
Where it forms: sedimentary deposits. If you start seeing calcite, quartz, dolomite in float, you are in the right ground. In the U.S., the densest reported localities are in Utah. Start trip planning there.
Common questions
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Find phosphorite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
