I hope someone tells us the answer, I'm stuck
It sounds like you are talking about obsidian.
You would expect to find an igneous rock with small crystals near the Earth's surface where the rock cools relatively quickly, such as in volcanic eruptions or magma intrusions that do not have much time to grow large crystals. These rocks are known as volcanic or extrusive igneous rocks.
The presence of tiny crystals in igneous rock indicates that the rock cooled quickly, resulting in the formation of small crystals. This suggests that the rock likely formed near or at the Earth's surface, like in a volcanic eruption. Rocks with larger crystals usually form deeper underground where cooling is slower.
Volcanic glass is an extrusive igneous rock. It forms when molten lava cools quickly on the Earth's surface, preventing the formation of crystals.
a porphyritic rock. This texture indicates that the rock underwent two stages of cooling: slow cooling deep underground (resulting in the large crystals) followed by faster cooling near the surface (resulting in the small crystals).
Geodes are rocks that are lined or filled with crystals. Pegmatites are rock formations that often exhibit extremely large crystals. Just a note--all rocks are composed of mineral crystals, with few exceptions. The crystals in some, however are just too small to see.
Intrusive rock normally has visible crystals. Extrusive igneous rock has small crystals. A black extrusive igneous rock with small crystals could be basalt.
The size of the crystals is a function of the rate of cooling of the molten rock. The faster the molten rock cools, the smaller the crystals will be.
You would expect to find an igneous rock with small crystals near the Earth's surface where the rock cools relatively quickly, such as in volcanic eruptions or magma intrusions that do not have much time to grow large crystals. These rocks are known as volcanic or extrusive igneous rocks.
Plutonic rock tends to have large crystals because it solidifies deep underground, where the overlying material insulates it so that it cools slowly, allowing time for large crystals to form. Volcanic rock tends to have small crystals (or to be amorphous) because it solidifies above ground, where air and water can cool it quickly by convection. Rapid cooling does not allow time for crystals to grow large. Plastic rock I don't know about.
rapid cooling, so that crystals do not form.
Most generally, an igneous rock with small crystals formed from the cooling of lava on the surface of the Earth would be classified as basalt.
The presence of tiny crystals in igneous rock indicates that the rock cooled quickly, resulting in the formation of small crystals. This suggests that the rock likely formed near or at the Earth's surface, like in a volcanic eruption. Rocks with larger crystals usually form deeper underground where cooling is slower.
No, shale is a sedimentary rock formed from the accumulation of clay, silt, or mud particles that have been compacted over time. It is not formed from volcanic activity like lava. Shale typically has very fine-grained particles, not crystals.
The presence of large and small crystals in igneous rock indicates a varied cooling history of the magma from which the rock formed. Large crystals suggest that the magma cooled slowly, allowing time for the crystals to grow, typically occurring in intrusive (plutonic) environments. In contrast, small crystals indicate rapid cooling, which is characteristic of extrusive (volcanic) environments. This mixed texture may point to a complex cooling process, such as the mingling of different magma types or changes in cooling rates during the rock's formation.
Extrusive igneous rock consists of mineral crystals that are not observable with the naked eye. Obsidian is an extrusive igneous rock (volcanic glass) where there technically are no mineral crystals.
All rock does not contain mineral crystals. Obsidian, or volcanic glass, in particular is a rock that has cooled so quickly from lava that mineral crystals were not able to form.
Andesite is an Igneous Rock. It has small crystals because it cooled quickly d;D