Mineral
A natural solid with a definite chemical formula and an ordered crystal structure. Quartz, calcite and diamond are minerals.
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From the pebble under your feet to the diamond in a crown.
We explain the stones of nature — how they form, where they are found and why some are precious — in plain language, with sources.
6,226IMA-approved mineral species
3great families of rock
108stone pages, and growing
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The value ladder
From the street to the diamond: what makes a stone precious?
Climb nine steps, from gravel sold by the tonne to museum-grade diamonds. At every step, what drives the value changes.
- Step 1
Everywhere, worthless
A pebble in a riverbed, a stone in a field. There are billions of tonnes of them and picking one up takes no effort. It is worth less than the cost of carrying it away.
- River pebbles
- Sand
- Step 2
Raw material by the tonne
Limestone, crushed stone, sand and gravel. Worthless one by one, yet by the million tonnes they are the basis of cement, concrete and roads. Value is mostly set by how far the quarry is from the city.
- Andesite →
- Augite (pyroxene) →
- Basalt →
- Biotite →
- Breccia →
- Chert and flint →
- +16
- Crushed stone
- Sand and gravel
- Step 4
Fine dimension stone and ore
Marble blocks, boron and chromium ores. Value comes from extracting large, flawless blocks, or from the metal or chemical that can be won from the rock.
- Step 5
Ornamental stone
Amethyst, agate, obsidian. Now stones are counted by the piece and the gram, not the tonne: colour, pattern and how it looks when polished matter.
- Step 6
Fine ornamental and collector stone
Turquoise, lapis lazuli, Oltu stone. They are rarer; the quality of colour, craftsmanship and the fame of the source raise the value.
- Step 7
Precious stone
Emerald, sapphire, zultanite. Hardness, clarity and play of light come together; value is now measured in carats (0.2 grams).
- Diaspore →
- Gold →
- Pallasite →
- Pearl →
- Spinel →
- Tanzanite →
- Emerald
- Sapphire
- Step 8
Top precious stone
Ruby and diamond. Besides colour, clarity, cut and weight, whether a stone has been treated and where it came from can multiply its value.
- Step 9
Museum-grade rarity
Coloured diamonds, historic jewels. Stones with few equals anywhere, whose value comes from their story and uniqueness; many are in museums, where everyone can see them.
- Coloured diamonds
- Historic jewels
The basics
Mineral or rock?
Rock
A natural mixture of minerals. Granite is a rock made of quartz, feldspar and mica.
Mineraloids and organics
Stones without a crystal structure (obsidian, opal) or made by living things (amber, pearl, Oltu stone).
The rock cycle
Stones have lives too: a cycle of millions of years
No stone stays the same forever. Magma cools, rocks wear away, sediments are squeezed, heat and pressure transform them, and in the end they melt again.
The Mohs hardness scale
Who scratches whom?
A mineral scratches anything softer than itself. The Mohs scale ranks 10 reference minerals; your fingernail, a copper coin and a pocket knife have their places too.
The scale is not evenly spaced: diamond is several times harder than corundum, just one step below it.
World map
Which stone is where?
The important localities of every stone, worldwide and in Türkiye. To protect sites, we show locations at regional level.
Stones of Anatolia
Stones that tell Türkiye’s story
From the obsidian trade of the Neolithic to a colour-changing diaspore found almost nowhere else on Earth.
Oltu stone
Erzurum’s black treasure: a kind of jet made from coalified wood, famous for its prayer beads.
Oltu, Erzurum, Türkiye
Diaspore
A rare mineral that looks greenish in daylight and pinkish under incandescent light; gem-quality material comes almost only from Muğla.
İlbir Mountains, Milas, Muğla, Türkiye · Gümüşdağ, near Ephesus, Türkiye
Meerschaum
A white stone light enough to float when dry and soft enough to carve: meerschaum, the raw material of Eskişehir's famous pipes.
Eskişehir, Türkiye
Colemanite
The backbone of Türkiye’s boron wealth: a calcium borate used to make heat-resistant glass and glass fibre.
Emet, Kütahya, Türkiye · Bigadiç, Balıkesir, Türkiye
Borax (tincal)
A sodium borate that dissolves in water and crumbles to white powder in dry air; one of the world’s key tincal deposits is at Kırka in Eskişehir.
Kırka, Seyitgazi, Eskişehir, Türkiye
Travertine
Hot springs turned to stone: the rock of Pamukkale's snow-white terraces and the walls of the Colosseum.
Pamukkale, Denizli, Türkiye · Denizli travertine basins (Honaz, Kocabaş), Türkiye
Tuff
Volcanic ash turned to stone: the soft rock that made Cappadocia’s fairy chimneys and rock-cut churches possible.
Göreme, Nevşehir, Türkiye · Derinkuyu, Nevşehir, Türkiye
Ignimbrite
The rock left by glowing avalanches of hot ash — the stone of the Seljuk gravestones of Ahlat.
Ahlat, Bitlis, Türkiye · Nevşehir Plateau, Cappadocia, Türkiye
Obsidian
Nature’s volcanic glass — the shiny black stone that gave the Stone Age its sharpest blades.
Nemrut Caldera, Tatvan, Bitlis, Türkiye · Göllüdağ, Niğde, Türkiye
Marble
Limestone reborn by heat and pressure — the favourite stone of sculptors and architects for thousands of years.
Marmara Island (Proconnesus), Balıkesir, Türkiye · İscehisar (Dokimeion), Afyonkarahisar, Türkiye
Basalt
The rock of the ocean floors and the Moon’s dark plains — the most common volcanic rock on Earth.
Kula-Salihli UNESCO Global Geopark, Manisa, Türkiye · Diyarbakır and Karacadağ, Türkiye
Chalcedony
A waxy-lustred stone made of quartz crystals far too small to see: the family name for agate, onyx and many other ornamental stones.
Sarıcakaya (Mayıslar–Sündiken Mountains), Eskişehir, Türkiye
Chromite
The only important ore of chromium, the metal that makes stainless steel resist rust; Türkiye is one of its leading producers.
Guleman (Alacakaya), Elazığ, Türkiye · Köyceğiz–Fethiye, Muğla, Türkiye
Halite (rock salt)
Table salt as a mineral: soft, soluble in water, breaking into cubes and lying underground in thick layers.
Lake Tuz (Tuz Gölü), Türkiye · Çankırı, Türkiye
Opal
Water-bearing silica with no crystal structure: in precious opal, tiny stacked spheres split light into flashes of rainbow colour.
Simav–Şaphane area, Kütahya, Türkiye
Andesite
The rock of volcanic arcs, named after the Andes — and the pink-grey stone of Ankara Castle.
Ankara Castle, Altındağ, Ankara, Türkiye · Gölbaşı, Ankara, Türkiye
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