Question 1

What is the difference between a rock and a mineral?

Accepted Answer

A **mineral** is a naturally occurring inorganic solid with a **definite chemical composition and crystal structure**; a **rock** is an aggregate of one or more minerals. Minerals are the ingredients; rocks are the mixture.

**What makes something a mineral.** Five conditions, all required:

**Naturally occurring** — synthetic equivalents are not minerals.

**Inorganic.**

**Solid** at ordinary conditions.

**A definite chemical composition**, expressible as a formula, though some vary within limits.

**An ordered internal crystal structure** — atoms arranged in a repeating three-dimensional lattice. **This is the defining property**, and it is why glass, having no ordered structure, is not a mineral.

**Quartz, feldspar, mica, calcite and olivine** are common examples.

**Rocks.** Aggregates, classified by **how they formed**:

**Igneous** — solidified from molten material. **Intrusive** rocks cool slowly underground, producing large visible crystals such as granite; **extrusive** rocks cool quickly at the surface, producing fine-grained rock such as basalt. **Crystal size records cooling rate**, which is a useful diagnostic.

**Sedimentary** — formed from accumulated particles or precipitated material, compacted and cemented. Sandstone, mudstone, limestone. These preserve **layering** and **fossils**, which igneous rocks do not.

**Metamorphic** — existing rock altered by heat, pressure or chemically active fluids **without melting**. Limestone becomes marble; mudstone becomes slate and then schist. Characteristically develops **foliation**, a banded or layered texture from minerals aligning under directed pressure.

**The rock cycle** connects them: any type can become any other through melting, erosion and deposition, or burial and metamorphism.

**Why the distinction is practically useful:** identifying a rock means identifying its constituent minerals and their arrangement, and a rock's properties follow from both.

**Terms frequently confused:** an **ore** is rock containing a mineral in economically extractable concentration; a **gemstone** is a mineral valued for appearance; **crystal** describes the ordered structure rather than a category of material; and **coal** and **amber** are organic, so their mineral status is anomalous.

Question 2

What is groundwater, and what is an aquifer?

Accepted Answer

Groundwater is water held beneath the surface in the spaces within rock and sediment; an aquifer is a body of rock permeable enough to yield usable quantities of it. Where it sits. Rainfall that

Question 3

Why do some volcanoes erupt explosively and others flow gently?

Accepted Answer

Because of the viscosity of the magma and how much dissolved gas it contains — and both are determined largely by silica content, which in turn depends on the tectonic setting. The mechanism. Magma

Question 4

What is the difference between an atom, a molecule, an element and a compound?

Accepted Answer

Two of these describe particles; two describe substances. Mixing the two categories is the source of nearly all the confusion. The particle terms: Atom — the smallest unit of an element that retains

Question 5

What is plate tectonics?

Accepted Answer

The theory that the Earth's outer shell is divided into rigid plates that move relative to one another over a weaker layer beneath — explaining earthquakes, volcanoes, mountain ranges and the

Question 6

How do mountains form, and why do they stop growing?

Accepted Answer

Mostly through tectonic collision thickening the crust, and they stop growing because erosion and gravity eventually balance uplift — so a mountain range's height reflects an equilibrium rather than

Question 7

How does fossilisation actually happen?

Accepted Answer

Rarely, and through several different processes — the important point being that fossilisation requires an unusual sequence of events, which is why the fossil record is a biased sample of past life

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