Rocks
Rocks may be divided into three broad groups as {Igneous rocks}, {Sedimentary rocks} and {Metamorphic rocks}.
Rock
Glossary
Igneous rocks
Igneous rocks, such as granite, dolerite and basalt, are those formed by the fusion of minerals under great heat and
Glossary
Metamorphic rocks
Metamorphic rocks such as slates and schists are those changed from igneous, sedimentary or from soils into metamorphic by pressure
Glossary
Gravel and crushed hard rock
Clean, well-graded gravel or crushed hard rock are both excellent, but somewhat expensive materials for hardcore.