Similarly, a rock with small crystals probably formed at or near the surface and cooled quickly. Sometimes, a rock will contain both aphanitic and phaneritic crystals in it. This means that something truly odd happened to the magma before it was erupted. Since we know that large crystals need time to grow, the magma must have spent some time deep underground.
But the smaller crystals mean that the rest of the cooling happened very quickly. If a rock has both crystal types, it means that the mamga spent some time in a magma chamber, where the large crystals grew, then was violently erupted onto the surface, where the small crystals were formed. We can simulate the growth of minerals using some common materials; just about everyone has grown salt and sugar crystals from a supersaturated solution. However, those experiments take more time than is usually available in the classroom, so we have developed a demonstration based on one given in Jackson, J.
Melting the mothballs and crayon mixture. Cooling the mothballs and crayon mixture. Before the demonstration: Fill one beaker with mL of water and place it on the hot plate; bring to a boil.
Crush one of the mothballs with the pliers and place it into a test tube; crush a crayon and add it to the test tube. Shake the test tube to mix the mothball and the crayon. Repeat, placing the other mothballs and crayons into separate test tubes. Igneous rocks do not contain any fossils. This is because any fossils in the original rock will have melted when the rock melted to form magma.
You may have done an experiment at school with a substance called salol. If molten salol cools slowly, you get big crystals. If it cools quickly, you get small crystals. Igneous rocks Igneous rocks are formed from molten rock that has cooled and solidified. What are igneous rocks like? Join our community of educators and receive the latest information on National Geographic's resources for you and your students.
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