ANALYSIS OF ORDOVICIAN LIMESTONES WITH REGARD TO THEIR USE AS CONSTRUCTION AGGREGATES

This study broadly examines the mineral constituents of limestone samples from various locations within the New Franklin, PA site of Valley Quarries, with respect to use as construction aggregate. Samples were analyzed in terms of composition, including percentage of carbonate and non-carbonate minerals present. The purpose herein was to identify mineral constituents (particularly deleterious ones), correlate mineral compositions to sampled stratigraphic layers, and interpret the aggregate’s potential industrial applications.

The stratigraphic units studied were the Stonehenge and Rockdale Run Formations of the Beekmantown Group. Class C coarse aggregate is extracted from these Lower Ordovician carbonates, although siliceous laminae and chert nodules are of common occurrence. Ten samples were collected encompassing the variations of the lithology in the analyzed sections. Acid-insoluble residues were described in terms of percent composition, visual observation, and XRD analysis.

Insoluble residue content ranged from 4.08% to 42.81%, with an average 14.78%. Limestone must be of at least 85% purity for Type C coarse aggregate, therefore the quality of rock extracted from this quarry is appropriate for the present industrial use. The primary deleterious materials present include quartz and microcline (potentially resulting in alkali-silica reactivity), clay minerals (kaolinite, illite), chlorite, and pyrite. These minerals are interpreted to be depositional remnants of weathered rhyolite and quartzite from nearby South Mountain.