Stone Mountain Field Trip - Historical Geology

GEOL1122 Field Trip

Sam Peavy & Dan Askren, Dept. Geology & Physics, Georgia Southwestern State University

Aplitic dike cross-cutting older Stone Mountain Granite.

Inclusion of gneiss within younger Stone Mountain Granite. The gneiss is
partially melted. Note the clots of tourmaline, surrounded by a white
bleached zone of Fe-depleted granite, at several locations near
the hammer.

Al, Lori, Jana & Abby debate the relative age of a gneiss
inclusion and surrounding granite

Another inclusion of gneiss within the younger Stone Mountain
Granite. Also, a younger light colored vein cross cuts the gneiss.

A light colored dike cross cuts the older Stone Mountain Granite.

An irregular, relatively coarse grained vein (left to right)
cross cuts an older, finer grained (aplitic) dike (top to bottom),
which in turn cross cuts the even older Stone Mountain Granite.

Pegmatite (very coarse grained granitic rock), composed chiefly
of alkali feldspar and quartz, cross cuts older granite.

Coarse grained dike (pegmatite), composed chiefly of pink
alkali feldspar and quartz, cross cuts older granite. Also,
a thin vein cross cuts the granite from left to right (parallel
to the pen)and is OFFSET by the pegmatite. The pegmatite, therefore,
is the youngest feature present.

Outdoor museum recounts quarrying history of Stone Mountain Granite.

Photos along Georgia's Fall Line