Virtual Rock Collection
Image above: Examples of different types of nonfoliated metamorphic rocks. Sources of individual rock images are derived from 3D models on Sketchfab with Creative Commons licensing; see same models below for creator credits and licensing details.
Nonfoliated metamorphic rocks lack foliated texture because they often lack platy minerals such as micas. They commonly result from contact or regional metamorphism. Examples include marble, quartzite, greenstone, hornfel, and anthracite.
Marble is low- to high-grade metamorphosed limestone or dolostone (both of which are carbonate rocks). They are composed of interlocked calcite or dolomite grains. Marble is very commonly carved in artwork.
Specimen of marble. Model by Edurock - Educational Virtual Rock Collection (Sketchfab; Creative Commons Attribution International 4.0 license).
Quartzite results from medium- to high-grade metamorphism of quartz sandstone. It is characterized by interlocking grains of quartz and can be differentiated from sandstone by the fact that individual grains do not fall off when the rock is rubbed. Original sedimentary structures may remain visible in quartzite.
Sample of pink quartzite from the teaching collections of the Paleontological Research Institution, Ithaca, New York. Longest dimension of specimen is approximately 9 cm (Sketchfab; Creative Commons Attribution-Share Alike 4.0 International license).
Original caption: "This quartzite comes from Sauk County, Wisconsin. It is 10 cm in longest dimension. The only mineral visible is purple quartz." Model by "rocksandminerals" (Sketchfab; Creative Commons Attribution 4.0 International license).
Greenstone results from low- to high-grade metamorphism of mafic igneous rock. Important minerals in greenstone include chlorite, epidote, and hornblende. Greenstone is greenish in color and fine grained. Some of the oldest known continental rocks are "greenstone belts."
Original caption: "Slightly metamorphosed basalt (greenstone) of Morrow Mountain State Park, NC. The basalt erupted ~550 Ma as part of an island arc prior to colliding with Laurentia as part of the Carolina Terrane." Model by Dr. Daren Nelson (Sketchfab).
Hornfel results from low- to medium-grade metamorphism of shale. Minerals in hornfel include micas, garnets, and quartz. Banding is sometimes evident, but is not associated with foliation. Hornfel is a very hard rock.
Sample with both hornfel (top) and granite (bottom). Original caption: "An example of contact metamorphism where granite intruded into shales. The shales metamorphosed into hornfels. The specimen is from Mt Cootha, Queensland, Australia." Model by UQ School of Earth and Environmental Sciences (Sketchfab).
Anthracite results from high-grade metamorphism of coal. It is black in color and shiny. Anthracite is highly valued for burning due to its high carbon content.
Sample of anthracite. Model by EduRock - Educational Virtual Rock Collection (Sketchfab; Creative Commons Attribution 4.0 International license).