No and yes, technically. Pumice does form from cooling magma (cools extremely fast, in fact, almost instantly). Because of this rapid cooling the crystals are extremely small to the point of many geologists considering pumice to be microcrystalline or glassy, meaning there wasn't enough time for actual crystals to form.
Mineral crystals in rock can be interlocked when forming or metamorphosed, or simply cemented together. Rocks with interlocking crystals tend to resist breakage by a force better than cemented rock.
No, not all extrusive igneous rocks contain visible crystals. Some extrusive rocks, such as obsidian and pumice, cool so quickly that mineral crystals do not have a chance to form, resulting in a glassy texture instead.
Igneous rocks can have both small and large crystals, depending on how quickly they cool. If an igneous rock cools slowly beneath the Earth's surface, it can form large crystals, while rapid cooling at the Earth's surface or in an eruption can result in small or no visible crystals.
Obsidian lacks crystals because it is a type of volcanic glass that cools too quickly for mineral crystals to form. Pumice and scoria lack crystals due to their porous nature and high gas content, preventing the growth of crystalline structures during cooling.
Mostly, it depends on cooling time. If a rock cools very rapidly, a smooth texture is formed as the atoms quickly arrange themselves into a fairly smooth crystalline pattern. Think of obsidian; it cools very fast and has such small crystals looks like black warped glass. However, if a rock was formed below the Earth's surface (intrusively) like in a pluton, it will cool more slowly and will be rougher and have larger crystals.
Pumice does not have crystals. It is made of glass.
Mineral crystals in rock can be interlocked when forming or metamorphosed, or simply cemented together. Rocks with interlocking crystals tend to resist breakage by a force better than cemented rock.
no
Pumice doesn't have crystals at all, as it cools too quickly for them to form.
Pumice is made of glass. Glass forms when molten rock cools too quickly for crystals to form.
No, not all extrusive igneous rocks contain visible crystals. Some extrusive rocks, such as obsidian and pumice, cool so quickly that mineral crystals do not have a chance to form, resulting in a glassy texture instead.
Igneous rocks can have both small and large crystals, depending on how quickly they cool. If an igneous rock cools slowly beneath the Earth's surface, it can form large crystals, while rapid cooling at the Earth's surface or in an eruption can result in small or no visible crystals.
Rocks are normally composed of interlocking mineral crystals or clasts. It is rare for metamorphic rocks to be porous and as such there is likely to be very little if any air in them. An example of a very porous rock due to the presence of gasses coming out of solution from a lava is pumice.
Granite is a dense, non-porous rock with visible mineral grains. Pumice is a light rock filled with holes left by gas bubbles and generally no visible grains.
Obsidian lacks crystals because it is a type of volcanic glass that cools too quickly for mineral crystals to form. Pumice and scoria lack crystals due to their porous nature and high gas content, preventing the growth of crystalline structures during cooling.
Pumice is so fine grained, it actually doesn't have a grain--because it is a natural volcanic glass. The rough texture is caused by the vesicular nature of the rock--trapped pockets of gas bubbles with sharp glassy edges.
No. Pumice cools very rapidly above the surface. It is a glassy rock. Glass forms when lava cools too quickly for crystals to form.