Rocks can be divided into three basic classifications: igneous, sedimentary, and metamorphic. In early history of the birth of the crust, the earth surface was fusion, so the largest volume of the crust was igneous rocks. However, after years and years, the hard igneous rocks were weathered, so the largest volume of the crust became sedimentary rocks. Active plate tectonics on Earth brought rocks into a new high-temperature and high-pressure environment. Minerals must adjust their crystal structure, and the rocks that changed during these solid-state processes are metamorphic rocks.

"Black Rock" is how people call basalt in Penghu. In fact, the color of basalts in Penghu are not completely black. Moreover, the texture is not exactly the same. How to distinguish the basalts we see can be understood from the physical organization and chemical composition.
1. Physical organization classification:
The basalts can be divided into (1) dense basalt and (2) vesicular basalt.
2. Classification of chemical composition:
The basalts can be divided into (1) silicic basalt and (2) alkali-basalt.
The simple resolution table is as below: