Earth and Environmental Science 11–12 · Year 11

Identifying minerals by hardness, streak, lustre, cleavage, acid test and specific gravity

Module 1: Earth’s Resources

PracticalLow risk

The idea

A mineral is identified from a fixed set of physical properties that follow from its composition and crystal structure, applied through a dichotomous key.

Safety card

Low riskAn adult supervises

Hazards

1 mol/L hydrochloric acid on skin or eyes
sharp specimen edges and glass plate
galena is a lead sulfide mineral; the streak test turns it into powder

Controls

safety glasses
one drop from a dropping bottle
rinse skin with water
wipe the streak plate, do not blow dust
galena is streaked and weighed by the teacher only, wearing gloves
after the galena tests, wash the streak plate, bench and weighing water container down with dilute detergent solution and wash hands

Note

Chemicals are used, and galena is a lead compound: lead and lead salts are on the Chemical Safety in Schools (CSIS) Volume 2 Appendix F list of chemicals to be used with caution, whose use is largely reserved for science teachers, and areas where lead salts have been used should be washed down. Follow the NSW Department of Education CSIS package, Section 1 (including the CSIS 1.7 risk assessment requirement) and Appendix F, read the Safety Data Sheet for each chemical and complete a RiskAssess risk assessment before the lesson.

What you need

mineral set of at least eight: quartz, calcite, feldspar, mica, galena, pyrite, magnetite, gypsum, halite (labelled for the teacher, unlabelled for learners)
unglazed porcelain streak plate, glass plate, a steel nail or knife blade and a fingernail as the hardness reference points
hand lens, magnet, dropping bottle of 1 mol/L hydrochloric acid
balance to 0.1 g, beaker of water and thread for weighing in air and in water
a dichotomous key prepared for the set (the Earthlearningidea Identifying minerals activity shows how such a key is built and read)

How to do it

Record colour and lustre (metallic or non-metallic) for each unknown.
Scratch each mineral across the streak plate and record the streak colour; the teacher streaks the galena, because the test powders it, and washes the plate down afterwards.
Test hardness in order against the fingernail (2.5), the glass plate, and the steel nail or knife blade (steel 6.5, Geoscience Australia), and bracket the Mohs value: gypsum is scratched by a fingernail, calcite is not but does not scratch glass, and quartz scratches both glass and steel.
Look for cleavage planes or fracture with the hand lens; test with the magnet.
Put one drop of 1 mol/L hydrochloric acid on a fresh surface and record fizzing (carbonate present).
Weigh the specimen in air, then suspended in water (skip halite, which dissolves; the teacher weighs the galena); specific gravity = m_air / (m_air − m_water).
Work through the dichotomous key and name the mineral; check against the teacher list and record which property settled each identification.

What you should see

Calcite fizzes with acid, is scratched by the steel nail but not by a fingernail, and shows three cleavage directions; quartz scratches glass and shows no cleavage; galena has a grey streak, metallic lustre and cubic cleavage. Specific gravity from the two weighings: a quartz specimen weighs 62 % of its air mass in water (SG 2.65), galena 87 % (SG 7.5), so the water reading alone separates the heavy sulfide from the silicates. Every mineral in the list differs from the others in at least one of these tests, so the key can separate the whole set; the learner records which property settled each identification.

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; streak is more reliable).
Hardness means how easily a mineral breaks (that is toughness; hardness is scratch resistance).

Curriculum references

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

Earth and Environmental Science Stage 6 Syllabus (2017), NESA; current, replaced by the 11–12 Syllabus (2025) from 2028EES11-8 EES11/12-3 EES11/12-4 EES11/12-5
Earth and Environmental Science 11–12 Syllabus (2025), NESA; to be implemented from 2028, not yet taughtEES-11-02
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

All Concept Studio activities