Classify rocks by their formation

Start with a formation claim

Imagine three specimen cards. Card A records material that cooled from a melt. Card B records loose grains that became bound together. Card C records an existing solid rock whose minerals and texture changed while it remained solid. Their formation histories support igneous, sedimentary and metamorphic classifications respectively. The cards are fictional evidence, not photographs or measurements collected by the browser.

Before opening the investigation, draw each history as a starting material, a named process and an ending material. Circle the evidence that establishes the process. Then cover the history and ask whether a specimen’s color alone would recover it. A rock name should summarize supported observations and interpretation, not merely the color you expect.

Keep composition and texture separate

Composition describes what a rock contains. Texture describes the sizes, shapes and relationships of its components. Record them in separate columns when comparing specimens. Identifying quartz in a sample does not by itself establish the origin of the whole rock: the grains’ relationships and geological context matter too.

Igneous rocks form by solidification of melt. Magma is molten material below Earth’s surface; erupted molten material is called lava. Slower cooling commonly permits larger crystals, whereas rapid cooling can produce fine grains or glass. These are useful tendencies, not a stopwatch: the browser has no cooling-rate control and cannot calculate crystal size. USGS explanation of igneous formation.

Select Magma and Cool and solidify. Explain the arrow before capturing it. Now keep that pathway and choose Igneous rock as the initial material. The model stops because its cooling rule starts with magma. Cooling an already solid rock is not sufficient evidence that a new igneous rock formed. This restricted rule does not claim that real solid rocks cannot lose heat.

Produce sediment before lithifying it

Clastic sedimentary rocks contain particles derived from earlier material. Lithification turns loose sediment into rock; compaction rearranges and packs grains, while mineral cement can bind them. Chemical precipitation and accumulated biological material provide other sedimentary origins, which this browser does not simulate. Therefore its Compact and cement route is a selected clastic example, not the definition of every sedimentary rock. National Park Service explanation of sedimentary rocks.

Select Loose sediment and Compact and cement. Compare the output with Magma and Cool and solidify. Both routes end with a rock, but their input materials and processes differ. In your notes, replace the vague phrase “it became hard” with the specific process supplied by each case.

The Weather and deposit operation bundles weathering, erosion, transport and deposition into one teaching step. It does not predict particle size, dissolved material, transport distance or the environment of deposition. In a real investigation those would require separate evidence. Here the bundled result is a deposit of loose sediment that can enter the selected lithification rule.

Inspect evidence rather than memorizing a visual shortcut

For an educator-provided specimen or image, make a labeled sketch showing grain boundaries, apparent grain sizes and any visible arrangement. Add a scale if one is supplied; do not estimate a real grain size from an unscaled picture. Separate direct descriptions from inferences. “Several rounded particles surrounded by finer material” records different information from “a river deposited this rock.” The latter requires an argument.

If access to physical specimens is unavailable, use the three opening cards and create your own contrasting drawings. Ask a partner, or your future self with the captions hidden, which distinctions the drawings actually encode. A sketch of dots alone might represent grains in several categories. Improve the evidence caption rather than assuming that the intended answer is visible.

The browser verifies only its programmed category transitions. It does not identify a real specimen or evaluate your sketch. Your evidence record should state what additional observation would strengthen the interpretation and what remains uncertain.

Transfer to an unfamiliar record

A new card describes loose sand whose spaces later acquire mineral cement. Another describes a melt that solidifies with crystals. Both resulting materials contain crystals. Should they receive the same formation category merely because crystals are present?

Check the rock-formation transfer

No. The first record describes clastic lithification and supports a sedimentary origin; the second describes solidification from melt and supports an igneous origin. Crystal presence alone does not distinguish these histories. The explanation needs the relationship between grains, cement and the documented formation process.

Save two supported transitions and one unsupported pairing. Explain why the stopped trace is a limit of the selected rule, and name a sedimentary origin that this investigation leaves out.