What is the texture of pegmatite?
What is the texture of pegmatite?
A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than 1 cm (0.4 in) and sometimes greater than 1 meter (3 ft). Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic composition to granite.
What rock has a glassy texture?
Obsidian
Obsidian is the common rock that has a glassy texture, and is essentially volcanic glass. Obsidian is usually black.
Which are the 4 types of texture for igneous rocks?
Igneous textures are used by geologists in determining the mode of origin of igneous rocks and are used in rock classification. There are six main types of textures; phaneritic, aphanitic, porphyritic, glassy, pyroclastic and pegmatitic.
What are the 3 textures of 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)
Is glassy a texture?
If a rock looks like a block of (colored) glass, with no visible mineral crystals, it has a glassy texture. Superficially, a glassy texture suggests cooling that was so extremely fast that no crystals could form. However, composition is also vitally important.
Is glassy texture intrusive or extrusive?
Igneous Textures
| 1. Textural Terms Based On Crystal Size | |
|---|---|
| Intrusive Textures | Extrusive Textures |
| Pegmatitic: Slow cooling plus high water content | Glassy: Fast cooling plus high silica content |
What type of rock looks like glass?
obsidian
obsidian, igneous rock occurring as a natural glass formed by the rapid cooling of viscous lava from volcanoes. Obsidian is extremely rich in silica (about 65 to 80 percent), is low in water, and has a chemical composition similar to rhyolite. Obsidian has a glassy lustre and is slightly harder than window glass.
What type of rock is glass?
igneous rock
Obsidian (/ˌɒbˈsɪdiən/; /əb-/) is a naturally occurring volcanic glass formed when lava extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock….
| Obsidian | |
|---|---|
| Specific gravity | c. 2.4 |
| Optical properties | Translucent |
| Other characteristics | Texture: Smooth; glassy |
| References |
What are glassy igneous rocks?
Description. A glassy igneous rock consists of dense volcanic glass. The very porous, foamy variety is called Pumice. The most important rock type belonging to this group is: obsidian.
What is the texture of stone?
Natural stone has a variety of surface textures, including polished, honed, leathered, and brushed. While polished and honed surfaces are the most popular nowadays, leathered and brushed surfaces are gaining popularity due to their ability to instantly bring a unique flair to an otherwise sleek and glossy surface.
What is a fine texture?
Definitions of fine-textured. adjective. having a smooth, fine-grained structure. synonyms: smooth-textured smooth. having a surface free from roughness or bumps or ridges or irregularities.
Is pegmatite intrusive or extrusive?
intrusive igneous rock
Pegmatite is called an intrusive igneous rock because it forms when magma solidifies under the Earth’s surface. In contrast, when magma solidifies outside the Earth’s surface, it forms an extrusive igneous rock.
