Welded tuff is a type of pyroclastic rock. A pyroclastic deposit consists of fragmented material that is formed from explosive volcanic activity or from aerial expulsion from a volcanic event. These pyroclasts may be deposited in the form of pyroclastic flows [a dense, ground-hugging cloud of ashy material], forming ignimbrites (Greek for “fire cloud material”).… Continue reading Welded Tuff
Rhyolite is an igneous, extrusive volcanic rock high in silica forming typically in continental arc settings. The flow-banding in this sample is caused by the friction of the viscous magma in contact with a solid rock surface or by compaction, causing flattening and welding of shards and pummice. [Be prepared for pictures of a bunch… Continue reading Flow-banded rhyolite
As a geologist, not only do you have to be good in math, chemistry, physics, history, and writing, but you also kind of need to be decent at art. These are thin sections of magmatic rocks with my accompanying petrographic sketches. For a relatively small little circle, these guys take a really long time to… Continue reading Art of Geology
Thin section of dunite under XPL. Dunite is a type of peridotite that contains over 90% olivine and may either be found in ophiolitic complexes or xenoliths in basalt lavas. Note the ‘bubble’ texture of the vibrant birefringent olivine grains at the top and bottom of the image, and the serpentine (gray and white) and… Continue reading Dunite
Thin sections of lunar basalt (3.15-3.35 Ga) viewed under plane polarized light and cross-polarized light. Sample contains olivine, clinopyroxene, and plagioclase. Images by author
Horseshoe Harbor near Marquette, MI Midcontinent rift, baby! Just look at all these volcanic rocks.