Final answer:
The sharp-surfaced lava rock formed by the irregular fracture of solidified basaltic lavas is known as scoria, which has a cinder-like appearance due to its high vesicle content.
Step-by-step explanation:
The basaltic lavas that solidify at their surface before ceasing to flow fracture irregularly, producing a sharp-surfaced lava rock named scoria. Scoria is characterized by its rough surface texture, sharp edges, and often red-brown coloration. It is a type of basalt igneous rock which is formed from the cooling of lava, being rich in mafic magma and often containing over 50% vesicles, resulting in its cinder-like appearance.
Basalt makes up most of Earth's oceanic crust and is found on planets that have experienced extensive volcanic activity. Its quick cooling on the Earth's surface leads to the formation of extrusive, or volcanic, igneous rock with very tiny crystals. Contrasting this is the longer-cooled, coarse-grained plutonic, or intrusive, igneous rock like granite, which has larger, easily visible crystals.