Science and Technology K–6 · Year 3

Testing rocks: scratch, streak, fizz and soak

Science understanding: Earth and space sciences

PracticalLow risk

The idea

Rocks and minerals have observable, testable properties, hardness, streak colour, reaction with acid and water absorption, that tell us what they are made of and what they are useful for.

What you need

rock set: sandstone, granite, limestone or marble, slate or shale, quartz, plus 2 unknowns, each piece about 100 g, which is the mass the soak-test figures below are worked for
scratch tools: fingernail (hardness about 2.5), a copper coin such as an old 1c or 2c piece, or a copper pipe offcut (about 3 to 3.5), steel nail (about 5.5), a glass tile with ground edges (about 5.5) on the Mohs scale
unglazed white porcelain tile for streak
white vinegar in a dropper bottle
hand lens
kitchen balance reading to 0.1 g, bowl of water, paper towel (a balance reading only to 1 g cannot show the gain on granite, quartz or slate, which the figures below put under 0.5 g)

How to do it

Look at each rock with the hand lens and record grain size, colour and whether you can see crystals or layers.
Scratch each rock with the fingernail, then the coin, then the nail. Record the softest tool that makes a scratch. Then try to scratch the glass tile, lying flat on the bench, with each rock. Together these bracket the hardness.
Drag each rock across the porcelain tile and record the streak colour.
Put three drops of vinegar on each rock and watch with the hand lens for 30 seconds. Record fizz or no fizz.
Weigh each dry rock, soak it in water for 10 minutes, pat the surface dry and weigh again. Record the mass gained.
Use the four results to name the two unknowns from the reference set.
Match each rock to a use (building stone, roof slate, cement, gravel) and explain the property that suits it.

What you should see

Limestone and calcite marble give off bubbles of carbon dioxide in vinegar, but slowly: vinegar is a much weaker acid than the dilute hydrochloric acid geologists use, so watch with the hand lens, and expect only a few small bubbles on marble. Dolomite marble may show none at all, so no fizz on a marble is a result to record, not a failed test. The others do not fizz. Quartz (hardness 7) scratches glass and is not scratched by the nail; calcite-rich limestone and marble (calcite is hardness 3) are scratched by the nail. Quartz and granite are about as hard as the unglazed porcelain tile or harder, so they leave no streak and may scratch the tile instead; record that as no streak. Porous sandstone gains the most mass on soaking. If every pore of a 100 g chip of density 2.3 g per cubic centimetre (volume 43 cm3) filled, pore space of 5 to 15 percent would take up 2.2 to 6.5 g of water; a 10-minute soak fills only part of it, so the gain is less. A 100 g granite chip (volume 38 cm3) with under 1 percent pore space could take up under 0.4 g, which is why the balance has to read to 0.1 g and why granite, quartz and slate are recorded as a gain too small to measure rather than as a zero. The mass gained divided by the rock's volume estimates how much open pore space it has, for the rocks whose gain the balance can resolve.

What changes

What you change: rock type
What you measure: hardness bracket, streak colour, fizz, mass gained on soaking
What you keep the same: same tools
same number of vinegar drops
same soaking time

Common misconceptions

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

Hard rocks are heavy rocks (hardness and density are different properties).
All rocks are the same underneath; only the colour differs.
Vinegar fizzes on any rock if you wait long enough.

Safety card

Low riskLearners carry it out

Hazards

steel nail point
rock dust
vinegar in eyes
glass tile edges

Controls

scratch away from the body
no hammering or breaking rocks
safety glasses for the vinegar test
wash hands

Note

Household chemicals only. Risk assessment before the lesson using the NSW Department of Education Chemical Safety in Schools package (CSIS 1.7 Risk Assessment) or Primary RiskAssess.

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 and Technology K-6 Syllabus (2017), current, taught until 2026; Stage 2 content under this outcome: 'investigate how the properties of natural and processed materials influence their suitability and use', which the last step (matching each rock to a use) addresses; the syllabus has no Stage 2 content on testing rock properties; code read from the syllabus document on 22 September 2026ST2-7MW-T
Science and Technology K-6 Syllabus (2017), current, taught until 2026; Stage 2 content under this outcome names rocks in the surface-change content ('investigate why the Earth's surface changes over time as a result of natural processes and human activity', including 'identify evidence of natural changes in landforms, rocks or fossils'), which is the Earth and Space content the rock set touches, as in the two other entries built on AC9S3U02; code read from the syllabus document on 22 September 2026ST2-10ES-S
Science and Technology K-6 Syllabus (2017), current, taught until 2026; code read from the syllabus document on 22 September 2026ST2-1WS-S
Science and Technology K-6 Syllabus (2024), implemented from 2027; NESA's timeline is 2026 plan and prepare and 2027 start teaching, and schools may choose to implement it during 2026; the 2024 Stage 2 content has no content point on testing the properties of rocks or minerals, so the 2024 mapping is to the data outcome the recorded test results sit under; code read from the outcomes page and the content read from the Stage 2 content page on 23 September 2026ST2-DAT-01
Australian Curriculum v9AC9S3U02AC9S3H02AC9S3I03

Sources

The pages the author read to write this activity.

All Concept Studio activities