Final answer:
Yes, it is true that a rock can be composed of almost entirely one mineral. Rocks like limestone and basalt can be examples of rocks predominantly composed of calcite and feldspar or pyroxene, respectively.
Step-by-step explanation:
The statement that a rock can be composed of almost entirely one mineral is true. Rocks can be a complex mixture of different minerals, but some rocks are indeed composed predominantly of a single mineral. Rocks can be classified into three basic types: igneous, sedimentary, and metamorphic.
For instance, limestone is often primarily composed of the mineral calcite. The composition and formation of rocks are fundamental concepts in geology, which studies the various processes that result in the formation of these different rock types. Some rocks, like the igneous rock known as basalt, are often made up almost entirely of a single mineral, such as feldspar or pyroxene.