Christianstead Gneiss

OFR54 Bedrock Geologic Map of the Delaware Piedmont

The Piedmont rock units in Delaware, and bedrock geologic map of Schenck et al. (2000) are revised in this report based on new rock geochemistry, geochronometric data, petrography, and recent detailed mapping. Major revisions include:

OFR55 Delaware Geological Survey Petrographic Data Viewer

Petrography is a branch of geoscience focused on the description and classification of rocks, primarily by microscopic study of optical properties of minerals. A thin sliver of rock is cut from a sample, mounted on a glass slide, ground to approximately 30 microns (0.03mm), and viewed under a microscope that uses polarized light. By observing the colors produced as plain polarized light and crossed (90 degrees) polarized light shines through the minerals, petrologists can determine the minerals that comprise the sampled rock.

Outcrop Ca44-d2: The Christianstead Subdivision

Outcrops between Hidden Valley Drive and Farmhouse Road. The Christianstead subdivision is underlain by interlayered mafic and felsic gneiss with large pegmatites. The felsic gneiss, in the northwestern half of this subdivision, is deformed granodiorite, seen as massive igneous layers with only rare crinkle folding. There are a few “bright eye” textures on the west end of this subdivision, which is all underlain by granodiorite.

Christianstead Gneiss

Coarse-grained, foliated granodioritic gneiss. Major minerals are biotite, microcline, plagioclase, and quartz. Includes thin layers of fine-grained foliated amphibolite plus large pegmatites.

GM13 Geologic Map of New Castle County, Delaware

This map shows the surficial geology of New Castle County, Delaware at a scale of 1:100,000. Maps at this scale are useful for viewing the general geologic framework on a county-wide basis, determining the geology of watersheds, and recognizing the relationship of geology to regional or county-wide environmental or land-use issues. This map, when combined with the subsurface geologic information, provides a basis for locating water supplies, mapping ground-water recharge areas, and protecting ground and surface water.