Free Stone Identifier by Photo —
What Stone Is This?

How to Identify Stone — What the AI Looks For

When you upload a photo to our free stone identifier, the AI analyses the same visual properties a geologist or stone merchant would examine. Understanding these properties helps you take better photos and interpret your results more confidently.

Grain Size and Texture

Grain size is one of the strongest clues for building stone. Coarse-grained stones like granite show individual crystals (quartz, feldspar, mica) visible to the naked eye. Fine-grained stones like basalt or slate have grains too small to see without magnification. Sedimentary stones like sandstone show rounded or angular sand grains cemented together. A close-up photo of surface texture is essential for accurate identification.

Colour, Veining, and Pattern

Colour alone is not always reliable — many stones share similar hues. However, colour pattern is very informative: granite shows speckled crystals; marble shows flowing veins; slate shows parallel layering; sandstone may show cross-bedding or iron-stained bands. Note whether the pattern is uniform, banded, speckled, or veined.

Surface Finish

Finish affects appearance but also hints at stone type. Polished surfaces are common on granite and marble countertops. Honed (matte) finishes show on limestone and some granites. Split-face or natural cleft surfaces are typical of slate and flagstone. Bush-hammered textures appear on some paving stones. Mention the finish in your notes.

Fossils and Shells

Visible fossils immediately identify sedimentary origin. Limestone and chalk often contain shell fragments, crinoids, or coral. Fossiliferous limestone is common in building stone from coastal quarries. If you see fossils, mention them — this narrows identification to specific sedimentary types.

Stone Identification Tests You Can Do at Home

While our AI works from photos alone, providing physical test results in the notes field significantly improves your identification.

The Acid Test

A drop of white vinegar on limestone, marble, travertine, or chalk causes immediate fizzing — these are all carbonate stones. Dolomite reacts only when scratched or powdered. This test definitively confirms or eliminates carbonate building stone in 10 seconds. Always test an inconspicuous spot.

The Scratch Test (Mohs Hardness)

Granite and quartzite (Mohs 6–7) scratch glass easily. Marble and limestone (Mohs 3–4) do not. Slate is approximately Mohs 2.5–4. Knowing whether your stone scratches glass immediately narrows the possibilities for countertop and paving stone.

The Magnet Test

Most building stone is non-magnetic. Weak attraction may indicate magnetite content in some basalts or iron-rich sandstones. Strong magnetic response suggests the material is not typical dimension stone.

Common Building Stones and How to Identify Them

These are the stones people most frequently upload to our identifier:

Granite

The most popular countertop stone worldwide. Coarse-grained with visible speckles of quartz (grey), feldspar (white/pink), and mica (black/silver). Very hard (Mohs 6–7), does not react to acid. Polished granite shows high reflectivity. Common colours: black, grey, pink, red, and white varieties.

Marble

Metamorphosed limestone with characteristic veining and swirls. Softer than granite (Mohs 3–4), reacts to vinegar. White Carrara marble is the classic; coloured varieties include green, pink, and black. Honed marble has a matte appearance; polished marble is highly reflective.

Limestone

A sedimentary carbonate stone — white, cream, yellow, or grey. Often contains visible fossils or shell fragments. Key test: fizzes immediately with vinegar. Used for building facades, flooring, and paving. Travertine is a porous form of limestone.

Sandstone

Visible sand grains cemented together. Colour varies — red/orange (iron oxide), yellow-brown, white, or grey. Gritty texture. Used for paving, building, and landscaping. Indian sandstone paving is one of the most common uploads to our identifier.

Slate

Fine-grained metamorphic stone that splits into thin flat sheets. Grey, black, green, or purple. Natural cleft surface. Used for roofing, paving, and wall cladding. Softer than granite; does not react strongly to acid unless calcareous.

Quartzite

Metamorphosed sandstone — extremely hard (Mohs 7), often white or grey with glassy appearance. Increasingly popular as a countertop alternative to marble. Does not react to acid. Often confused with marble but much harder.

Choosing Stone for Your Project

Once identified, consider these practical factors for building and landscaping use:

• Outdoor paving — choose frost-resistant, low-porosity stone (granite, slate, porphyry). Avoid soft limestone in freeze-thaw climates.
• Countertops — granite and quartzite are most durable; marble etches with acid (lemon, wine). Soapstone is soft but heat-resistant.
• Wall cladding — limestone and sandstone are traditional; ensure adequate fixing for weight.
• Driveway gravel — crushed granite, limestone, or slate chips; consider colour stability and compaction.
• Pool surrounds — choose non-slip honed or flamed finish; avoid polished marble (slippery when wet).

Using Our Specialist Identifier Tools

For raw rocks and field specimens rather than building stone, use our rock identifier. For gemstones in jewellery, try our gemstone identifier. For crystals and mineral specimens, use our crystal identifier or mineral identifier.