Black vertical stripe of rock
MCHD’s soil engineers over at Tai and Associates noticed an interesting feature as the excavators were digging out the area for the new Preschool Buildings on the new campus. Note in this picture the white, chalky soil on the left, the orange sandstone on the right, and the vertical black stripe running up the red Carolina clay in between.
This black stripe of rock is known as a Diabase Dike. According to Mr. Matt Ryan of Tai & Assoc, after the formation of the Durham Triassic Basin (250 to 200 million years ago), magma shot through the ground up to the ground surface vertically, forming the diabase dikes. The magma cooled into fractured rock.
“In this picture, you can actually see portions of the Triassic siltstone that are blackened from the heat of the magma. Over geologic times, the dikes go through a chemical and mechanical weathering process, and the portion near the surface becomes softer, and weathers into soil. The soil is sometimes sandy, but is usually a soft, plastic silt with boulders,” says Mr. Ryan.
- Diabase Dike
“The dikes in the Durham Triassic Basin are usually between 5 and 50 feet wide, about 1 to 20 miles long, usually have a heading that is a little east of north-south, and have about a 15 degree inclination fromvertical.”
Pretty cool, huh?
different rock formed by different cooling rates of the magma
