Mineral or Rock: The Difference Explained With Stone Examples
A mineral is a substance of defined composition; a rock is an assemblage of minerals (or of glass or organic matter). Granite, lapis lazuli, jade, jasper: where does each one belong?
Key points
| Mineral | A single substance, with defined composition and structure |
|---|---|
| Rock | An assemblage of minerals (sometimes glass or organic matter) |
| Granite | Quartz, feldspars, micas: a rock |
| Quartz | A mineral (SiO2) |
| Lapis lazuli | A rock (lazurite, calcite, pyrite, among others) |
| Jade | Two different rocks depending on the deposit: jadeitite and nephrite |
| Three families | Igneous, sedimentary, metamorphic |
The difference in one sentence
A mineral is a natural substance of defined chemical composition and ordered crystalline structure, such as quartz. A rock is a natural assemblage of grains of several minerals (or of fragments, glass or organic matter), such as granite, which contains quartz, feldspar and mica.
A comparison helps: a mineral is an ingredient, a rock is a cake. A cake can be made from a single ingredient, such as limestone, which is almost entirely calcite: it is then a monomineralic rock. But most rocks are polymineralic. The study of minerals is called mineralogy; that of rocks, petrology.
Examples from the world of stones
| Stone | Mineral or rock? | Composition |
|---|---|---|
| Quartz, amethyst, citrine | Mineral | SiO2 |
| Labradorite | Mineral | Plagioclase (feldspar) |
| Larvikite | Rock | Feldspars with blue sheen, with other minerals (Larvik rock, Norway) |
| Granite | Rock | Quartz, feldspars, micas |
| Lapis lazuli | Rock | Lazurite (blue), calcite, pyrite (golden flecks) and other minerals |
| Jade | Rock, of two types | Jadeitite (jadeite) or nephrite (amphibole actinolite-tremolite) |
| Green aventurine | Rock | Quartzite with green mica flakes (fuchsite) |
| Unakite | Rock | Altered granite: pink feldspar, green epidote, quartz |
| Obsidian | Vitreous volcanic rock | Glass, without ordered crystals |
| Lava stone | Volcanic rock | Vesicular basalt |
| Jasper | Rock, or a variety of quartz | Microcrystalline quartz with iron oxides and clay |
| Marble | Rock | Recrystallized calcite (or dolomite) |
| Chalcedony, agate | Microcrystalline variety of quartz | Quartz and a little moganite |
| Amber, jet | Neither one | Fossil resin and wood (organic matter) |
Jasper and agate are borderline cases: their grains are all of the same species, quartz, but very fine and mixed with impurities. Depending on the references, they are classed either as mineral varieties or as rocks: sources differ, and both presentations can be defended. See our pages on jade, lapis lazuli, larvikite and green aventurine.
Why this changes the way you look at a stone
Because a rock does not have a single hardness or a single density. Lapis lazuli is often given as 5 to 5.5, but that figure sums up minerals of different hardness: lazurite 5 to 5.5, pyrite 6 to 6.5, calcite 3. The surface therefore wears unevenly. Jade, for its part, is extremely tough because its tiny fibres interlock like felt. Rocks are therefore often more resistant to impact than their minerals taken on their own. Conversely, a poorly cemented rock crumbles.
This also explains the variety of colours within a single “stone”: the colour of a granite depends on the proportions of its minerals, pink with a lot of potassium feldspar, grey with more quartz and plagioclase.
The three families of rocks
| Family | Origin | Examples |
|---|---|---|
| Igneous (magmatic) | Cooling of magma or lava | Granite, basalt, obsidian |
| Sedimentary | Accumulation and hardening of sediments | Limestone, sandstone, chalk |
| Metamorphic | Transformation by heat and pressure, without complete melting | Marble, quartzite, schist |
These three families are linked by the rock cycle: a rock can be eroded, buried, melted or transformed into another, in no fixed order. The details are in the pages on igneous rocks, sedimentary rocks and metamorphic rocks.
Trade words that mislead
- “Black granite”: in the trade, this name often covers gabbro, basalt or dolerite, not true granite.
- “Marble”: for a stonemason, any limestone hard enough to be polished. For a geologist, a limestone recrystallized by metamorphism.
- “Precious stone” and “semi-precious stone”: these expressions are used less and less, because they suggest that some stones are of lesser value. Professionals prefer “gem” or “coloured stone”.
- “Crystal”: a crystal is an ordered solid, not a precious stone. “Rock crystal” is colourless quartz; “crystal” glass is leaded glass.
Observing a granite in ten minutes
Take a piece of granite (a countertop, a pebble, a curb) and a magnifying glass. Look for grey, shiny grains with a glassy look: that is quartz; white or pink grains with flat faces that reflect light all at once: that is feldspar; small black or silvery flakes: that is mica. You have separated three minerals and you understand what a rock is. A steel nail scratches feldspar with difficulty but not quartz; do not scratch a valuable stone.
Frequently asked questions
Is quartz a rock?
No, it is a mineral (SiO2). But it makes up rocks such as quartzite and is part of the composition of granite and sandstone.
Is lapis lazuli a mineral?
It is a rock: it is made of blue lazurite, white calcite, golden pyrite and other minerals depending on the deposit.
Is jade a mineral or a rock?
The term covers two different rocks: jadeitite, made of jadeite, and nephrite, made of amphibole. Each is an aggregate of very fine fibres.
Is obsidian a mineral?
No. It is volcanic glass, a rock without an ordered crystalline structure.
Why are both rocks and minerals called stones?
“Stone” is an everyday term, with no precise scientific definition. Here it covers minerals as well as rocks or polished organic materials.
Also read
The meanings mentioned belong to tradition and symbolism. They are neither promises of results nor medical advice. Back to Mineralogy for beginners.