Which of the following is not one of the three types of rock? a. igneous b. sedimentary c. magma d. metamorphic

Correct answer is c ( magma) . 

There are three kinds of rock: igneous, sedimentary, and metamorphic. 

Igneous rocks. When the molten magma cools, it becomes solid. Rocks formed in this way are called igneous rocks. They are also called primary rocks. They are of two types- intrusive rocks and extrusive rocks.
∙. Extrusive rocks. When molten lava comes on the earth's surface, it rapidly cools down and becomes solid. Rocks formed in this way on the crust Eire called extrusive igneous rocks. For example, basalt.
∙ Intrusive rocks. Sometimes the molten magma cools down deep inside the earth's crust. Solid rocks so formed are called intrusive igneous rocks. Since they cool down slowly they form large grains. For example, granite.

2. Sedimentary rocks. Small fragments of rocks are called sediments. These sediments are transported and deposited by wind, water, etc. These loose sediments are compressed and hardened to form sedimentary rocks. For example, sandstone is made from grains of sand.

3. Metamorphic rocks. When igneous and sedimentary rocks Eire subjected to great heat and pressure they change into metamorphic rocks. For example, clay changes into slate and limestone into marble.