Question

minerals
2. The igneous rock formed by very fast cooling of magma is
a. pumice
b. obsidian
c. granite
3. This rock can float in
d. limestone​

Answer 1

Answer:

2. Granite

Granite, coarse- or medium-grained intrusive igneous rock that is rich in quartz and feldspar; it is the most common plutonic rock of the Earth's crust, forming by the cooling of magma (silicate melt) at depth.

Obsidian may be also the answer

Extrusive igneous rock

Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock. Obsidian is produced when felsic lava extruded from a volcano cools rapidly with minimal crystal growth.

3. Pumice

Extrusive volcanic rock

Pumice is a type of extrusive volcanic rock, produced when lava with a very high content of water and gases is discharged from a volcano. As the gas bubbles escape, the lava becomes frothy. When this lava cools and hardens, the result is a very light rock material filled with tiny bubbles of gas.

Explanation:

Extrusive igneous rocks cool and solidify more quickly than intrusive igneous rocks. They are formed by the cooling of molten magma on the earth's surface. ... Basalt is a common extrusive igneous rock and forms lava flows, lava sheets and lava plateaus. Some kinds of basalt solidify to form long polygonal columns.

The Canadian Shield of North America contains huge outcroppings (surface rocks) of granite. Dacite is an extrusive igneous rock. The principle minerals that make up dacite are plagioclase, quartz, pyroxene, or hornblende. Obsidian is a very shiny natural volcanic glass.