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
Fracture you should know this lol
The climate 250 mya was very tropical, so maybe those fossils could've been found there even w/o continental drift
