What does fine grained texture mean?
Fine-grained textures generally indicate magmas that rapidly cooled at or near the Earth’s surface. Fast cooling prevents crystals from growing very large. The cutoff between fine- and coarse-grained textures is about 1 mm.
What is a coarse-grained texture?
Coarse-grained textures generally indicate magmas that slowly cooled deep underground. Slow cooling gives crystals enough time to grow to easily seen sizes (i.e., larger than 1 mm). The first-formed crystals tend to have regular shapes because they grow freely into the surrounding liquid.
What is an example of a fine grained rock?
Fine grained rocks, where the individual grains are too small to see, are called aphanitic. Basalt is an example. The most common glassy rock is obsidian.
How is a fine grained texture formed?
Magmas that erupt as lava onto the earth’s surface cool and solidify rapidly. Rapid cooling results in an aphanitic igneous texture, in which few or none of the individual minerals are big enough to see with the naked eye. This is sometimes referred to as a fine-grained igneous texture.
What is the difference between aphanitic and fine grained?
Crystalline rocks with mineral grains that cannot be distinguished from one another without magnification have an aphanitic igneous texture. Intrusive igneous rocks thus have coarse-grained, or phaneritic, textures with visible crystals, and extrusive igneous rocks have fine-grained, or aphanitic, texture.
What are the 4 textures of igneous rocks?
Igneous Rock Textures
- COARSE GRAINED TEXTURE (PHANERITIC), mineral grains easily visible (grains several mm in size or larger)
- B) FINE GRAINED TEXTURE (APHANITIC), mineral grains smaller than 1mm (need hand lens or microscope to see minerals)
- C) PORPHYRITIC TEXTURE (MIXED FINE AND COARSE)
What does a porphyritic texture mean?
Porphyritic – This texture describes a rock that has well-formed crystals visible to the naked eye, called phenocrysts, set in a very fine grained or glassy matrix, called the groundmass.
What is the difference between Aphanitic and fine-grained?
What are the three main classes of rock?
There are three kinds of rock: igneous, sedimentary, and metamorphic. Igneous rocks form when molten rock (magma or lava) cools and solidifies. Sedimentary rocks originate when particles settle out of water or air, or by precipitation of minerals from water. They accumulate in layers.
What are the 4 types of igneous rocks?
Igneous rocks can be divided into four categories based on their chemical composition: felsic, intermediate, mafic, and ultramafic.
What does Aphanitic fine grained texture look like?
Fine Grained Texture (Aphanitic), Mineral Grains Smaller Than 1mm (Need Hand Lens or Microscope to See Minerals) Aphanitic texture consists of small crystals that cannot be seen by the eye with or hand lens. The entire rock is made up of small crystals, which are generally less than 1/2 mm in size.
What are the 3 major texture categories?
Thus there are distinct igneous textures, distinct sedimentary texture, and distinct metamorphic textures. For the purposes of this exercise and routine classification, the kinds of minerals and their proportions, or MINERALOGY, are taken as the natural expression of composition.