Granite is typical of a larger family of granitic rocks that are composed mostly of coarse-grained quartz and feldspars in varying proportions. These rocks are classified by the relative percentages of quartz, alkali feldspar, and plagioclase (the QAPF classification), with true granite representing granitic rocks rich in quartz and alkali feldspar. Most granitic rocks also contain mica or amphibole minerals, though a few (known as leucogranites) contain almost no dark minerals.
Granite is nearly always massive (lacking any internal structures), hard, and tough. These properties have made granite a widespread construction stone throughout human history. Glacial polish is a characteristic of rock surfaces where glaciers have passed over bedrock, typically granite or other hard igneous or metamorphic rock. Moving ice will carry pebbles and sand grains removed from upper levels which in turn grind a smooth or grooved surface upon the underlying rock.The presence of such polish indicates that the glaciation was relatively recent (in geologic time scale) or was subsequently protected by deposition, as such polish will be subsequently lost due to weathering processes (such as exfoliation).
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