Why does granite have large, visible crystals while basalt has crystals too small to see?
AGranite is older, so the crystals had more time to grow over the centuries
BGranite cooled slowly deep underground, giving crystals time to grow; basalt cooled quickly at the surface
CGranite is made of different chemicals that naturally form bigger crystals
DBasalt's crystals were worn away by wind and rain
Crystal size depends on cooling rate. Granite forms deep underground where magma cools over thousands to millions of years, so crystals grow large. Basalt forms from lava that cools in days to weeks at the surface, leaving no time for large crystals.
Question 2 Short Answer
Obsidian is a volcanic glass with no crystals at all. What does this tell you about how it formed?
Think about your answer, then reveal below.
Model answer: Obsidian cooled so quickly that there was no time for any crystals to form at all. The atoms froze in place before they could arrange themselves into an orderly crystal structure.
Obsidian represents the extreme end of fast cooling. It often forms when lava contacts water or is ejected into cold air during an eruption.
Question 3 True / False
Magma and lava are the same substance — the only difference is location.
TTrue
FFalse
Answer: True
Magma is melted rock beneath Earth's surface. The moment it erupts and reaches the surface, it is called lava. The material itself is the same; only the name changes based on where it is.