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Given a scientific passage and an answer, generate a question for the given answer.

Passage: Underground water can be heated by magma. The hot water moves through cracks below Earth's surface. Hot water can hold more dissolved particles than cold water. The hot, salty solution has chemical reactions with the rocks around it. The water picks up more dissolved particles. As it flows through open spaces in rocks, the water deposits solid minerals. When a mineral fills cracks in rocks, the deposits are called "veins. " Figure below shows a white quartz vein. When the minerals are deposited in open spaces, large crystals grow. These rocks are called geodes. Figure below shows a "geode" that was formed when amethyst crystals grew in an open space in a rock. Answer: veins
Output:
What are the mineral deposits that fill in underground cracks called?