Metamorphic Staurolite Mica Schist ID'd
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This is the metamorphic rock
This is the metamorphic rock called mica schist (using 360 degree photography). Schists come with a variety of minerals. It is most easily recognized by having many visible, reflective micas--such as muscovite and/or biotite micas. Schist often contains some feldspars, quartz, and hornblende minerals too. Also, schist may contain garnet or staurolite minerals. Garnet and schist often have similar reddish-brown colors, and have similar hardnesses (about 7-7.5 on Mohs' scale) However, garnets form 12-sided dodecahedrons (sort of like a soccer ball, but without as many sides), and staurolites form elongated crystals that sometimes are twinned (they may grow together and intersect each other). There is high demand for relatively rare staurolite crystals that are twinned and intersect at 90 degrees. These form a cross-like structure that are popular with religious Christians. Be aware that some rock shops sell cross-shaped staurolites that are fake (consist of manufactured replicas).
Schist forms in a foliated, medium-grade metamorphic environment. This sample comes from the Blanchard Dam area on the Mississippi River--near Royalton, Minnesota, USA. The gravels below the dam are eroded out of the schist bedrock, and used to contain many staurolite minerals of moderate size--with some of them forming crosses. However, the site has become discovered by rockhounds, and it is often difficult to find sizable staurolites in the river gravels now. The river site has easy access, although it can be very hot in summer or very cold in winter (the river and ground will freeze and be covered by snow in the winter).
There is a progression to reach the metamorphic level of schist. Initially, the lowest-grade metamorphic rock begins as slate. Slate is fine-grain size and looks barely reflective--like an old-fashioned blackboard. Next is phyllite, with a slightly silky sheen to the flat surfaces on the rock--as you rotate the rock. This is because phyllite has microscopic muscovites that are all oriented in the same direction--on the flat, foliated surfaces of the rock. Again, the microscopic muscovites are too tiny to see individually (without a microscope). However, the collective number of microscopic muscovites in this rock, give the flat surfaces of phyllite that collective subtle shine or sheen. Schist is the medium-grade metamorphic rock that often has visible muscovite (which makes schist visibly sparkle--sort of like sequins on a dress). If the metamorphism continues, schist will change into gneiss.
Hello Rock People! This is Dave the Geology dude! Identification notes for this rock are below in this text. Please be aware that the only way to really learn rock identification, is to have hands-on experience. This is because visual experiences alone do not show properties like hardness, acid reactivity, density, and the range of variables that are common to each rock type. Note: if you don't like the music on this video, you can always turn off the sound and watch with your own music instead. Don't forget that Geology isn't rocket science--it's Rock Science! Please "like" and subscribe to this YouTube channel!
Music (YouTube Audio Library): Midnight Special (by E’s Jammy Jams)
Copyright by David Knoblach, 2023. All rights reserved
Schist forms in a foliated, medium-grade metamorphic environment. This sample comes from the Blanchard Dam area on the Mississippi River--near Royalton, Minnesota, USA. The gravels below the dam are eroded out of the schist bedrock, and used to contain many staurolite minerals of moderate size--with some of them forming crosses. However, the site has become discovered by rockhounds, and it is often difficult to find sizable staurolites in the river gravels now. The river site has easy access, although it can be very hot in summer or very cold in winter (the river and ground will freeze and be covered by snow in the winter).
There is a progression to reach the metamorphic level of schist. Initially, the lowest-grade metamorphic rock begins as slate. Slate is fine-grain size and looks barely reflective--like an old-fashioned blackboard. Next is phyllite, with a slightly silky sheen to the flat surfaces on the rock--as you rotate the rock. This is because phyllite has microscopic muscovites that are all oriented in the same direction--on the flat, foliated surfaces of the rock. Again, the microscopic muscovites are too tiny to see individually (without a microscope). However, the collective number of microscopic muscovites in this rock, give the flat surfaces of phyllite that collective subtle shine or sheen. Schist is the medium-grade metamorphic rock that often has visible muscovite (which makes schist visibly sparkle--sort of like sequins on a dress). If the metamorphism continues, schist will change into gneiss.
Hello Rock People! This is Dave the Geology dude! Identification notes for this rock are below in this text. Please be aware that the only way to really learn rock identification, is to have hands-on experience. This is because visual experiences alone do not show properties like hardness, acid reactivity, density, and the range of variables that are common to each rock type. Note: if you don't like the music on this video, you can always turn off the sound and watch with your own music instead. Don't forget that Geology isn't rocket science--it's Rock Science! Please "like" and subscribe to this YouTube channel!
Music (YouTube Audio Library): Midnight Special (by E’s Jammy Jams)
Copyright by David Knoblach, 2023. All rights reserved
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