Mineral and rock identification lab – hardness, streak, lustre, cleavage, density and the acid test
GeographyEarth's Structure & LandformsAges 15–16Virtual lab
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A virtual practical with ten unknown mineral samples. Scratch each one with a fingernail, a copper coin, a glass plate and a steel file to place it on the Mohs scale, rub it on a streak plate, look at its lustre, break it with a hammer to see cleavage or fracture, measure its mass and its volume by water displacement to work out its density, drop dilute hydrochloric acid on it and hold a magnet near it. Each result fills the observation table and lights up a dichotomous key that names quartz, feldspar, mica, calcite, gypsum, halite, galena, pyrite, magnetite and hematite. A rock screen classifies fourteen rocks as igneous, sedimentary or metamorphic from their texture under a hand lens, and a third screen shows the seven crystal systems as crystal models you can turn.
Lesson: Minerals and rocks: identifying minerals by their physical properties; igneous, sedimentary and metamorphic rocks; crystal systems
What it shows
Minerals are naturally formed solids with a definite chemical composition and an ordered crystal structure, so each one has its own set of physical properties. Geologists identify them with simple tests: hardness on the Mohs scale, the colour of the powder (streak), lustre, how the mineral breaks (cleavage or fracture), density and reactions such as fizzing in dilute acid. Rocks are made of minerals; their texture shows how they formed: interlocking crystals from cooling magma (igneous), cemented grains and fossils (sedimentary) or crystals lined up by heat and pressure (metamorphic). The model uses typical values; real samples vary.
How to use
On the Minerals tab, pick a Sample and press the Tests one by one; each result fills the table and the key. Read the cylinder to find the volume, calculate the density and check it, then name the sample. On the Rocks tab, pick a Rock, use the Hand lens and Dilute HCl, and choose its Rock group. On the Crystal systems tab, choose a Crystal form and drag it to turn it.
Parameters you can change
- Screen Minerals, Rocks, Crystal systems
- Sample set (which mineral gets which letter) 1–6
- Show the identification keys
- Label the samples with their names
Questions to explore
- Which two tests separate quartz from calcite, even though both can be white and glassy?
- A sample has a mass of 26.5 g and raises the water from 20.0 mL to 30.0 mL. What is its density?
- Why do granite and basalt have such different crystal sizes although both come from magma?
