Non-foliated rocks are metamorphic rocks without a layered structure, forming under uniform pressure or due to mineral composition. Common types include marble, quartzite, hornfels, granofels, and amphibolite, each with unique textures and properties.
What are Non-Foliated Rocks?
Non-foliated rocks do not have platy or sheet-like structures but have random arrangements of the mineral components.
Types of Non-Foliated Rocks:
There are two types of non-foliated rocks –
- The first type consists of thermal or contact metamorphic rock called hornfels (singular). They generally occur in narrow belts around intrusive bodies and may originate from any type of parent rock.
- The second type develops if the newly formed metamorphic minerals are equidimensional and so do not grow in any preferred orientation.
Some non-foliated rocks are,
Marble:
It consists of fine to coarsely crystalline rock containing calcite and dolomite. Marbles form from limestones and dolostones as their parent rocks. The texture of marble usually features an interlocking mosaic growth of calcite or dolomite. In its purest form, marble appears white, but various impurities create beautifully variegated colors. Organic matter may tint marbles gray or black.
Quartzite:
It is metamorphic equivalent of quartz sandstone composed of about 80 percent or more quartz. Quartz grains are interlocking each other. Quartzites are very hard rocks and break across the quartz grains.
Granofels:
A comprehensive term for any isotropic rock (a rock with no preferred orientation).
Hornfels:
Fine-grained, non-foliated, dense, and usually dark rocks form near the contacts of igneous intrusions. Interlocking mineral grains create a mosaic. Hornfelses commonly break into splintery fragments with translucent edges resembling horns. Geologists most frequently apply the term to baked shale. This rock exhibits a characteristic texture called hornfelsic texture.
Amphibolite:
It is dark colored medium to coarse grained rock. Amphibolites contain mostly plagioclase and hornblende and often some biotite as well. Sometimes the long axes of hornblendes lie in planar arrangement causing linear schistosity. Rocks rich in ferromagnesian minerals such as basalt are the parent rock for amphibolites.
