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