Eduqas A-Level Geology Elements, minerals and rocks: atoms, silicates, identification and the rock cycle

What this concept actually demands

Elements, minerals and rocks is the foundation of Eduqas A-Level Geology: everything later (igneous classification, Bowen's reaction series, sedimentary and metamorphic petrology, economic geology) assumes the named minerals and rocks and the chemistry behind them. The examiners test two linked skills here: explaining how atomic structure and bonding control the properties of minerals, and identifying minerals and rocks from their physical properties in hand specimen, which is the practical skill at the heart of Component 1.

This guide walks through the five clusters of the concept in a sensible build order, then sets out the exam patterns Eduqas repeats. Each cluster has a matching dot-point page with practice questions; this overview ties them together.

Atomic structure and bonding

Minerals are built from a few rock-forming elements (oxygen and silicon dominate, then aluminium, iron, calcium, sodium, potassium and magnesium). Atoms have a nucleus of protons and neutrons with electrons in shells; the atomic number (protons) defines the element, and isotopes are atoms with the same protons but different neutrons (chemically identical, but the basis of radiometric dating and stable-isotope palaeoclimate proxies). Bonding is ionic (electron transfer, for example halite), covalent (electron sharing, for example diamond and the framework of quartz) or metallic (a sea of delocalised electrons, for example native copper). The master idea is that bond strength controls hardness and the directionality of bonding controls cleavage.

Silicate structures and mineral groups

Every silicate is built from the silicon-oxygen tetrahedron. As tetrahedra share more corner oxygens they polymerise from isolated units (olivine), through single chains (pyroxene), double chains (amphibole) and sheets (mica), to continuous frameworks (quartz and feldspar). More sharing lowers the silicon-to-oxygen ratio and raises weathering resistance. The non-silicate minerals are grouped by anion: carbonates (calcite, dolomite), oxides (magnetite, hematite), sulphides (pyrite, galena, chalcopyrite, sphalerite), halides (halite, fluorite) and native elements (gold, copper, diamond).

Identifying minerals by physical properties

No single property identifies a mineral; you combine them. Hardness on the Mohs scale (fingernail 2.5, coin 3.5, knife and glass 5.5), cleavage (directions and angles) versus fracture (quartz conchoidal), lustre (metallic or non-metallic), the unreliable colour versus the reliable streak (powder colour, for example hematite's red-brown), habit, density by heft (galena and magnetite feel heavy), and special tests (the magnet for magnetite, dilute acid for calcite). This is the practical skill Component 1 examines directly.

Practical tests and fieldwork

A small field kit (hardness references, acid bottle, magnet, streak plate, hand lens) resolves most specimens, and rocks are classified by combining texture and mineralogy (igneous interlocking crystals, sedimentary bedded grains, metamorphic foliated or recrystallised). Observations are recorded with labelled field sketches (better than photos because they select, annotate and interpret), oriented samples, logs and dip-and-strike readings, always with a scale and grid reference. A-level students complete a minimum of four days of fieldwork; Eduqas has no separate graded endorsement, so these skills are examined within Components 1 and 3.

The rock cycle

The three rock families (igneous, sedimentary, metamorphic) are linked by the rock cycle: crystallisation, weathering, erosion and transport, deposition, lithification, burial and metamorphism, melting and uplift, with no single fixed route. Solar energy and gravity drive the surface processes (weathering, transport, deposition); the Earth's internal heat drives the internal processes (metamorphism, melting, tectonic burial and uplift). The cycle is the framework that organises every later topic.

How this concept is examined

A typical Eduqas profile for Elements, minerals and rocks:

• Knowledge and explanation questions (Component 2). How bonding controls hardness and cleavage, the silicate polymerisation series and weathering, and the energy sources of the rock cycle.
• Identification questions (Component 1). Identifying a mineral or rock from listed properties (a magnetic, grey-streaked oxide is magnetite; a fizzing, rhombic-cleaved mineral is calcite), the single most common task in the specimen paper.
• Practical and recording questions (Components 1 and 3). Describing the tests to identify a rock, and why a labelled field sketch beats a photograph.
• Levels-of-response extended answers (Component 2). Tracing material through the rock cycle, and explaining how structure controls a suite of mineral properties, are predictable six-mark questions.

Check your knowledge

A mix of recall and application questions covering the whole concept. Attempt them under timed conditions, then check against the solutions.

1. State the two most abundant elements in the crust by mass and what they form together. (2 marks)
2. Define isotope and give one geological use. (2 marks)
3. Explain why quartz has no cleavage but mica has one perfect cleavage. (3 marks)
4. Describe how the silicate structure changes from olivine to quartz and the effect on weathering resistance. (4 marks)
5. Name the mineral group of calcite, galena, halite and magnetite. (2 marks)
6. State the field references for hardness 2.5, 3.5 and 5.5. (2 marks)
7. Explain why streak is more reliable than colour, with an example. (2 marks)
8. State the minimum fieldwork days for the Eduqas A-level and how practical skills are assessed. (2 marks)
9. State which rock-cycle processes are driven by the Sun and gravity and which by internal heat, with one example each. (2 marks)