Note 9 — THE GEOLOGY OF MT. PHILO STATE FOREST PARK

A quartzite is either a metamorphic or sedimentary rock consisting of fragments of the mineral quartz (SiO₂) which are cemented together by silica (quartz). The combination of quartz fragments held together by quartz cement creates a very hard rock which oftentimes will break across the fragments rather than around them. The quartzites of the Park area are primarily of a sedimentary origin. For a description of the three major rock groups, of which the sedimentary and metamorphic groups are two, see footnote, D.A.R. State Park, page 6. A dolostone is a sedimentary rock composed of fragmental, concretionary, or precipitated dolomite (a mineral of chemical composition, CaMg(CO₃)₂) of organic or inorganic origin.