fills cracks in rocks are calledveins. Figure 3.24shows white quartz veins. When the
minerals are deposited in open spaces, large crystals can form. These special rocks are called
geodes.Figure3.25shows ageodethat was formed when amethyst crystals grew in an open
space in a rock.
Figure 3.24: Quartz veins formed in this rock. ( 31 )Figure 3.25: An amethyst geode that formed when large crystals grew in open spaces inside
the rock. ( 29 )
Lesson Summary
- Mineral crystals that form when magma cools are usually larger than crystals that
form when lava cools. - Minerals are deposited from salty water solutions on Earth’s surface and underground.