Science 7–10 · Year 8

Sorting a rock kit into igneous, sedimentary and metamorphic

Science understanding: Earth and space sciences (NSW Stage 4 focus area: Change)

PracticalMedium risk

School laboratory, not for home

In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

The idea

How a rock formed is written in its texture: interlocking crystals from cooling melt, cemented grains or layers from deposited sediment, and aligned bands or sheets from heat and pressure.

Safety card

Medium riskA teacher supervises

Setting: In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

Hazards

1 mol/L hydrochloric acid drops (irritant to eyes)
sharp rock edges and glass tile

Controls

safety glasses for the acid test
one drop only, rinse the specimen and wipe up
steel nail handled by the point away from the hand

Note

Write the risk assessment before the lesson under CSIS 1.7 (Risk Assessment, a pre-requisite for risk control) of the NSW Department of Education Chemical Safety in Schools package (Section 1, 2021 Technical Update), or through RiskAssess; keep the Safety Data Sheet for every chemical with the class register.

What you need

1 class rock kit with named hand specimens: granite, basalt, pumice, obsidian, sandstone, conglomerate, limestone, shale, slate, schist, gneiss, marble (12 specimens, one set per group of 3)
1 hand lens (x10) per learner
1 dropper bottle of 1 mol/L hydrochloric acid (about 10 mL) per group for the carbonate test
1 steel nail, 1 copper coin or copper strip and 1 glass tile per group for scratch tests
1 identification key with the three texture questions: interlocking crystals or glass, grains or fossils or layers, bands or sheets or sugary recrystallised texture

How to do it

Cover the labels. For each specimen record with the hand lens: crystals interlocking or separate grains; grain or crystal size (under 1 mm, 1 to 5 mm, over 5 mm); visible layers or bands; holes (vesicles); glassy surface; fossils.
Put one drop of acid on a fresh surface of each specimen and record fizzing (carbonate present).
Test whether a steel nail scratches the specimen and whether the specimen scratches glass.
Work through the key to assign igneous, sedimentary or metamorphic and a name; then uncover the labels and score the group.
For any wrong call, write which observation misled the group and what test would have settled it.

What you should see

Granite shows interlocking crystals over 1 mm (no fizz, scratches glass); basalt is dark with crystals too small to see; pumice is full of vesicles and floats; obsidian is glassy with curved fracture. Sandstone shows separate sand grains that rub off, conglomerate pebbles in a matrix, shale fine layers that split, limestone fizzes strongly with acid and may show shell fragments. Slate splits into flat sheets and rings when tapped, schist glitters with aligned mica flakes, gneiss shows light and dark bands, marble fizzes and has a sugary crystalline texture. Limestone and marble both fizz, and basalt and slate are both dark and fine-grained; texture (grains against interlocking crystals) and sheet-like splitting separate each pair. The learner knows it worked when every fizzing specimen was called a carbonate rock and every interlocking-crystal specimen without fizz was called igneous or high-grade metamorphic.

What changes

This activity lists no variables to change, measure and keep the same.

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Dark rocks are igneous and light rocks are sedimentary; colour does not sort rocks, texture does.
Rocks are single substances; most are mixtures of minerals.
Crystals mean the rock is valuable; all of granite is crystals.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Science 7-10 Syllabus (2023), NSW Education Standards Authority (implemented from 2026; codes read at curriculum.nsw.edu.au on 22 and 23 September 2026)SC4-CHG-01 SC4-WS-01 SC4-WS-04
Australian Curriculum v9AC9S8U04AC9S8I03AC9S8I04

Sources

The pages the author read to write this activity.

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