There are lots of types of rock and each type has different properties and uses. For example, some are strong and hard but others are soft and sandy. Some rocks are harder than others. For example ...

Large crystals found in geodes and other rocks are relatively rare ... Minerals and gems are classified by their physical properties, including hardness, luster, color, density, and magnetism.

Their findings, published in Science Advances, suggest that the properties of rocks may contribute equally to the generation ...