Science · Rock textures
Edited by: Hitoiki Arcade / Hitoiki Learning team · Published: · Editorial policy
Rock and building-stone photographs show grains that may be conspicuous or too fine to distinguish. Before explaining their size, ask how those grains formed. The same explanation cannot be applied to every grain just because it is large.
Compare crystals growing from molten material with pre-existing fragments accumulating. The aim is to connect material to rock with short arrows, rather than memorize a list of names. No specialist prerequisite article or specimen collection is needed.
The first example asks about rock formed when magma cools and solidifies. Rock formed from molten rock material is igneous. Explain the answer with “molten material → cooling and solidification,” rather than “it is hard.”
Sedimentary rock, another choice, includes rock formed from accumulated material such as sand. Metamorphic rock is pre-existing rock changed by heat, pressure or other factors. Distinguish changes to solid rock from magma solidifying. Sediment is not the classification for the rock formed from magma either.
In the second example, “slowly underground” and “generally” matter. More time for crystal growth favors relatively large mineral grains. Granite is an example of intrusive igneous rock formed underground in this way.
Rapid cooling instead favors fine-grained or glassy textures, so “an entirely glassy texture” does not fit this prompt. Nor is grain size independent of cooling rate. However, a rock's present position at the surface does not establish where it cooled. Uplift and erosion can expose rock that formed underground.
The third example asks about rock formed mainly from consolidated sand: sandstone. Here, compare the sizes of deposited fragments rather than crystals growing in magma. Rock or mineral fragments are called clasts. Compaction and minerals cementing grains together can turn sand into rock.
Mudstone mainly involves finer particles, while conglomerate mainly involves larger gravel-sized clasts; neither matches “mainly sand.” Basalt is igneous, rather than the answer for consolidated sand. Sandstone can also include finer material, so do not silently replace “mainly sand” with “only sand.”
Granite and sandstone can both contain minerals such as quartz and feldspar. Yet granite has interlocking crystals, while sandstone has accumulated grains compacted and cemented together. Shared mineral names do not make their formation histories identical.
On paper, summarize the first two examples as “molten material → cooling → crystal growth,” and the third as “fragments → accumulation → consolidation.” When explaining large grains, check that you have not confused growth time with the size of deposited fragments. This reviews the three exercises; it is not a method for identifying an unknown stone from appearance alone.
Next, the related matter guide separates state from composition. The weather guide moves away from rock grains to compare rainfall depth and volume. Name the basis of comparison each time you change topics.
The practice button selects middle-school basic and standard questions on rocks and Earth's interior. Other matching questions are included beyond these three. First attach a short “because it formed by…” explanation to each answer, connecting the name with its reason before continuing.
TRY & READ
Compare the choices before opening the answer and explanation. Reading an example does not save a test answer or score.
Example 1 · Earth science: rocks and Earth’s interior
Answer: Igneous rock
Igneous rock forms from material that was molten.
Example 2 · Earth science: rocks and Earth’s interior
Answer: Large mineral grains
Slow underground cooling gives mineral crystals more time to grow, so intrusive igneous rocks often contain relatively large visible crystals. Crystal size is therefore a clue to cooling history. It does not by itself identify a different elemental composition.
Compare the time available for growth when explaining the texture.
Example 3 · Earth science: rocks and Earth’s interior
Answer: Sandstone
Clastic sedimentary rocks are classified by the sizes of their particles. Clastic particles are fragments produced from material such as broken rock. Sandstone consists mainly of consolidated sand-sized grains, so grain size is the relevant comparison.
Source checked: 2026-10-26
Source checked: 2026-10-26
Source checked: 2026-10-26
Source checked: 2026-10-26
Topics: Earth science: rocks and Earth’s interior. Range: Broader knowledge. Difficulty: Basic, Standard. These are selected initially. You can change these on the setup screen.
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