Complete the form to classify your rock
Choose observable properties, then select “Classify Rock.”
Why this match?
- No classification yet.
Alternative matches
- Alternatives appear after classification.
Rock observations
Formula used
The classifier uses weighted property matching rather than one fixed equation. Each matching feature adds points to a rock profile. Strong diagnostic clues receive larger weights. The highest scoring profile becomes the primary classification.
How to use this calculator
- Inspect a fresh rock surface when possible.
- Select texture, grain size, minerals, and structure.
- Add hardness, density, silica, and field-test clues.
- Choose a known family only when reasonably certain.
- Select Classify Rock and review alternatives.
- Export the result using CSV or PDF.
Rock comparison table
| Rock | Family | Typical texture | Common minerals | Useful clue |
|---|---|---|---|---|
| Granite | Igneous | Coarse | Quartz, feldspar, mica | Visible interlocking crystals |
| Basalt | Igneous | Fine | Pyroxene, plagioclase | Dark and dense |
| Sandstone | Sedimentary | Clastic | Quartz | Sand-sized grains |
| Limestone | Sedimentary | Crystalline or clastic | Calcite | Often reacts with acid |
| Marble | Metamorphic | Crystalline | Calcite | Non-foliated and acid-reactive |
| Gneiss | Metamorphic | Banded | Quartz, feldspar, mica | Strong compositional bands |
Understanding rock classification
Rock classification begins with careful observation of texture and composition. Texture describes crystal size, grain shape, layering, and visible structures. Mineral composition helps separate rocks with similar outward appearances. Igneous rocks form when molten material cools and solidifies. Slow underground cooling usually creates large interlocking crystals. Fast surface cooling produces small crystals or glassy textures. Vesicles can develop when gas escapes from fresh lava. Granite commonly contains quartz, feldspar, and mica crystals.
Recognizing sedimentary rocks
Sedimentary rocks usually form from deposited particles or chemical precipitation. Clastic rocks contain fragments produced by weathering and erosion. Grain size strongly helps distinguish shale, sandstone, and conglomerate. Limestone often contains calcite and may preserve fossils. A weak acid commonly produces visible fizzing on calcite-rich samples. Layering is common because sediment accumulates through repeated depositional events. Organic sedimentary rocks can contain concentrated plant material.
Recognizing metamorphic rocks
Metamorphic rocks develop when existing rocks experience heat and pressure. Mineral grains can recrystallize without completely melting the rock. Directed pressure may align minerals into foliation or bands. Slate develops from shale under relatively low metamorphic conditions. Schist contains larger aligned minerals at stronger metamorphic conditions. Gneiss commonly displays distinctive alternating light and dark bands. Marble forms when limestone recrystallizes into interlocking calcite crystals. Quartzite usually forms from quartz-rich sandstone under metamorphism.
Improving identification confidence
Reliable field identification combines several clues instead of one property. Fresh surfaces often reveal minerals better than weathered surfaces. Hardness testing can separate soft calcite from harder quartz. Density provides another useful comparison when samples look similar. Magnetism may indicate iron-rich minerals in some igneous rocks. Record uncertain observations instead of forcing a definite choice. This tool estimates likely matches rather than laboratory certainty. Thin sections and chemical tests provide stronger professional confirmation. Photographing samples beside a scale improves later comparison. Consistent field notes also make repeated classifications more dependable when available.
Frequently asked questions
Can this tool identify every rock?
No. It focuses on common representative rocks. Many rocks require microscopy, chemistry, or expert field context.
Which property should I check first?
Start with texture, grain size, structure, and obvious minerals. These properties quickly narrow the rock family.
Why does acid reaction matter?
Calcite commonly reacts with dilute acid. That clue strongly supports limestone, marble, or other carbonate-rich rocks.
What if I do not know the hardness?
Leave hardness blank. The classifier can still use texture, minerals, color, structure, and field clues.
Can weathering change the result?
Yes. Weathering can hide fresh colors, weaken minerals, and alter surfaces. A freshly broken surface usually improves observations.
What does confidence mean?
Confidence describes how well your selected properties match the leading profile compared with competing profiles.
Is the classification suitable for professional reports?
Use it as a screening aid. Professional reports should verify important samples using accepted laboratory or petrographic methods.