Science 7–10 · Year 8

Mineral identification: hardness, streak, lustre, cleavage and acid

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

Each mineral has fixed physical properties, so a short set of tests separates minerals that look alike and shows why rocks made of them behave differently.

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
glass tile edges and flying chips when a corner is tapped
galena is lead sulfide: its streak powder and dust contain lead
fine mineral dust from streak plates

Controls

safety glasses throughout, including the cleavage taps
single drops of acid, rinse and dry the specimen
no tasting of any specimen; halite is identified by its cubes and by dissolving in water
the teacher alone streaks the galena and measures its density while the learners watch and record; hands are washed afterwards, and the streak plates and bench are wiped with a damp paper towel, never brushed dry (CSIS Appendix F lists lead and lead salts among the chemicals to be used with caution, whose use is largely reserved for science teachers, and says areas where lead salts are used should be washed down to remove lead-containing dust)

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; CSIS Appendix F (chemicals to be used with caution) covers lead and lead salts, which is why the teacher handles the galena; keep the Safety Data Sheet for every chemical with the class register.

What you need

1 mineral kit per group: quartz, calcite, feldspar, mica (muscovite), galena, magnetite, halite, gypsum, talc, pyrite (10 specimens)
1 unglazed porcelain streak plate, 1 glass tile, 1 steel nail, 1 copper coin or copper strip per group
1 dropper bottle of 1 mol/L hydrochloric acid (10 mL) per group
1 bar magnet, 1 hand lens, 1 electronic balance (0.1 g) and 1 10 mL measuring cylinder (0.2 mL graduations) per group, with galena and quartz fragments small enough to fit it; 1 dropper of water

How to do it

Record colour and lustre (metallic or non-metallic; glassy, pearly, earthy) with the hand lens.
Rub the specimen on the streak plate and record the streak colour; note where it differs from the body colour (the teacher streaks the galena).
Test hardness in order: fingernail, copper coin, steel nail, glass tile; record the softest tool that scratches the specimen and whether the specimen scratches glass.
Look for flat cleavage faces and how many directions they show; test halite and calcite by tapping a corner with the nail to see the cleavage shape.
Put one drop of acid on calcite and on quartz, and a few drops of water on a small grain of halite; hold the magnet near magnetite and near pyrite.
Measure the mass and the water-displacement volume of the quartz fragment in the 10 mL cylinder and compute its density; the teacher does the same for the galena fragment while the group records. Run each measurement twice; the teacher washes hands after handling galena.

What you should see

Quartz scratches glass and the steel nail cannot scratch it; calcite is scratched by the steel nail but not by a fingernail, shows three cleavage directions (rhomb fragments) and fizzes with acid while quartz does not; talc is scratched by a fingernail, and so is gypsum (Geoscience Australia gives a fingernail a hardness of 2.5, enough to scratch gypsum); halite breaks into cubes and dissolves in the water drop. Galena has a metallic lustre and a steel-grey streak and is distinctly heavy: Geoscience Australia gives it a specific gravity of 7.4 to 7.6. The displaced volume is the difference of two readings, each read to about 0.1 mL on 0.2 mL graduations, so the volume of a 1 to 2 mL fragment is uncertain by up to 0.2 mL, 10 to 20 percent, and a single galena value can fall anywhere from about 6 to 9.5 g/cm cubed: far above quartz, but not precise enough to confirm 7.4 to 7.6. Pyrite leaves a black streak although its body is brassy (Geoscience Australia); magnetite pulls the magnet and pyrite does not; mica peels into flexible sheets (one perfect cleavage). Feldspar matches quartz on every test listed but one: it defeats the fingernail, the coin and the nail, scratches glass, leaves a white streak, does not fizz with acid and is not magnetic. The cleavage recorded in step 4 separates the two, because feldspar breaks along two flat directions meeting at about a right angle while quartz has no cleavage and breaks on curved surfaces. The learner knows it worked when talc and gypsum fall in the fingernail group, calcite between the fingernail and the nail, and feldspar and quartz both resist every tool while scratching glass and are then told apart by cleavage rather than by hardness, and when the two galena density readings agree within the cylinder's reading error (up to 0.2 mL on a 1 to 2 mL fragment, 10 to 20 percent).

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.

Colour identifies a mineral; quartz comes in many colours and pyrite looks like gold.
Hardness means how easily it breaks; hardness is resistance to scratching, cleavage is how it breaks.
Anything metallic-looking is a metal; galena and pyrite are compounds.

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 v9AC9S8U04AC9S8I03AC9S8I05

Sources

The pages the author read to write this activity.

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