Friday Field Foto #45: Glauconitic sandstone
It’s several days late, but I wanted to get my own green rock (or, at least, photograph of a one) in for St. Patrick’s Day (see some great green rocks from earlier this week from Ron, Silver Fox, Tuff Cookie, and Harmonic Tremors)
This week’s photo is from the Cambrian Bliss Sandstone in the Franklin Mountains of westernmost Texas. The greenish material is glauconite … an authigenic mineral that typically forms in marine shelf settings, thought to reflect very slow sedimentation rates. In this example, the glauconitic sandstone is actually reworked material (note the cross stratification).
To learn more about what glauconite actually is, how it precipitates in sedimentary rocks, and what it means, check out this paper from Chavez and Reid (2000; Sedimentary Geology, v. 136)