Answer:
A. Obsidian
Explanation:
It fits the property described in the question.
It cools so fast that no visible crystal or grain could form. It has high silica Composition, black and glassy. It is also used to make tools with sharp edges
The answer is true.
If they're close they're steep
If they're far the slope will be gentle
The most appropriate answer would be magma. Lava is a magma that reaches the Earth's surface, which is technically it is also a magma, and magma is located below the Earth's surface.
Lava at Earth's surface or magma below Earth's surface cools and harden to form mineral crystals.
A geologist studies the earth's history.
