Geometry and Geology
From geology's start as a science, geologists have studied the 3D
relationships of rocks. The geologic map has evolved to depict these
The stereo net is a graphical depiction of 3D relationships on a flat page or
computer screen. The net may look like a map, but it should more closely
be interpreted as centered on a particular point to show geometric relationships. Like a map, however, the stereonet takes three dimensions and displays them on two dimensions.
Planes become curved lines, and lines become points.
Stereo Net Geometry
Getting the plane orientation from the net
Lines on a geologic map:
- Solid lines are confidently located, while dashed lines are
- Thick likes are faults, while thinner lines are the contacts between
different rock units, either bedding planes or intrusive contacts for
- Fault: a surface across which rocks have moved.
- Fault plane: initially, and over a short distance, the fault
surface can be considered to be a plane. Later
deformations can deform the plane, and over long distances,
faults cannot remain planar, but we can view the fault plane as
the tangent at a point to whatever the true surface is.
- Bedding: the layering in sedimentary rocks, originally
horizontal with rare exceptions (such as deltas or dunes which
have cross bedding, and which the astute geologist will note). Changing in bedding
record deformation of the rocks.
- Bedding plane: initially, and over a short distance, the
surface can be considered to be a plane.
- Strike and dip and formats
Last revision 8/19/2013