Volume 30 Issue 8
Article, pp. 4-10 | Full
StraboTools: A Mobile App for Quantifying Fabric in Geology
Quantification of field observations is an essential step in making them reproducible and
shareable, but field geologists have few tools for quantifying field observations of important
features such as foliation intensity, crystal alignment, vesicle elongation, joint intensity,
and mineral proportions. Here we describe a mobile app, StraboTools, which offers two ways to
rapidly and objectively quantify these variables. The edge fabric tool examines grayscale
gradients in a photograph and summarizes them with the edge fabric ellipse. For deformation of a
homogeneous material with passive markers, this ellipse tracks the strain ellipse. Edge fabric
ellipses can be determined on the outcrop and make quick work (5 seconds) of formerly
time-consuming and subjective strain-analysis tasks (e.g., Fry and Rf /Φ
analysis). They are remarkably sensitive to subtle deformations that are difficult to see by
eye. The color index tool determines the proportion of any component in the photograph whose
grayscale level can be isolated (e.g., dark minerals in a granitic rock, feldspar phenocrysts in
a lava, or blue epoxy in a thin section). Estimating proportions by eye has poor precision and
accuracy; the color index tool is both accurate and precise if a suitable rock face is
available. These tools can be used with photomicrographs and aerial photographs as well as in
Manuscript received 22 Feb. 2020. Revised manuscript received 19 May 2020.
Manuscript accepted 22 May 2020. Posted 9 June 2020.
© The Geological Society of America, 2020. CC-BY-NC.
Search Google Scholar for
Search GSA Today