Final answer:
Geologists study texture and composition as two primary characteristics to identify rocks, where texture involves the arrangement of the rock's grains and composition examines the minerals within the rock option(d).
Step-by-step explanation:
To identify a rock, geologists study a multitude of characteristics, but two of the primary ones are texture and composition. Texture refers to the size, shape, and arrangement of the grains or crystals within the rock, which can be classified into various categories such as clastic, crystalline/chemical, foliated, or non-foliated.
This gives an indication of the rock's history and formation processes. For instance, whether the rock has a fine or coarse grain can tell us about the conditions under which the rock was formed, such as the speed of cooling in igneous rocks.
Composition, on the other hand, analyzes the minerals the rock is made of, which can sometimes be observed with a hand lens or may require microscopic examination. The mineral composition can provide valuable clues about the rock's origin, the conditions of formation, and the rock's potential uses.
The various tests and observations enable geologists to classify the rock according to established categories in rock and mineral guides.