Weathered Vishnu Schist - Grand Canyon
"The Vishnu Group had its beginnings about 2 billion years ago in Precambrian time . . . This is the metamorphic rock now exposed at the bottom of the canyon in the Inner Gorge. Geologists call this dark-colored, garnet-studded layer the Vishnu Schist." Wikipedia
I liked how this looked like molten wax, even though it is some of the hardest rock.
I rafted with Arizona Raft Adventures AZRA
Thanks to SascoAZ for this answer to why this is named Vishnu Schist
"Geologists frequently name rock layers after surrounding landmarks (especially if the landmark is near an outcrop of the layer that is a good representation of the type). For example, the Hermit Shale layer in the canyon is named for Hermit Canyon where that rock layer is easily reached and where it was first scientifically described in detail.
Each of the rock layers that you mention derived their name from nearby canyon buttes and mesas. Specifically the Vishnu Schist was named by geologist Charles Walcott in the 1880s after Vishnu Temple, a prominent rock formation on the north side of the canyon near Cape Royale. The Brahma Schist was named by geologists Campbell and Maxson in the 1930s after Brahma Temple, a butte overlooking Bright Angel Canyon. I am not sure who named the Rama Schist (probably Campbell and Maxson), but it probably derived its name from Rama Temple, a rock spire near Vishnu Temple. All of these landmarks can be seen from the major overlooks on the South Rim.
The logical next question is how did these mesas and buttes get their names in the first place? Many of the canyon's landmarks were named by geologist Clarence Dutton who published one of the earliest (and best) detailed geologic studies of the canyon in 1882. Dutton believed that the canyon was such an important and impressive feature on the planet, that the names of its features should reflect all the world's cultures and thus he chose many names from mythologies and legends from around the world. Other examples of canyon landmarks named in this way are Wotan's Throne, Cheops Pyramid, Budda Temple, Solomon Temple, Jupiter Temple and Tower of Ra (all of these are major buttes, spires or mesas in the canyon).
Arizona resident, frequent Grand Canyon visitor and hiker, and historian who has researched and written about scientific studies in the canyon.
For an excellent overview of the early canyon geologists and their impact on how we view the canyon today, I recommend the excellent book "How the Canyon Became Grand" by Stephen Pyne
Dutton's classic work (where many of the formations were officially named for the first time) is "Tertiary History of the Grand Canon District" (published the United States Geological Survey in 1882 and republished by the University of Arizona Press in 2001)"