They are associated with the late stages of granite intrusions and the minerals formed in pegmatites literally had the time to enjoy the benefits of a slow crystallization process from a rich chemical stew produced by the cooling granite.
For an alternate hypothesis, see the link below.
Pegmatite rocks are known for having large crystals that form without a particular pattern. These rocks are often found in granite and have crystals that can be several centimeters to meters in size. The lack of clear crystal orientation in pegmatite is often due to the rapid cooling of the magma that forms them.
Calcite is the mineral commonly found in both limestone and marble. Both rocks are formed primarily from calcite crystals.
Large crystals can be found in diorite, typically consisting of plagioclase feldspar and amphibole minerals. These crystals are formed from the slow cooling of magma deep within the Earth's crust, allowing for the growth of larger mineral grains.
diamond
The largest crystals on Earth are found in the Cave of the Crystals in Naica, Mexico. These selenite crystals can reach sizes of up to 39 feet (12 meters) in length and weigh several tons. They formed under unique conditions of high temperature and high mineral concentrations in the cave.
Pegmatite rocks can contain some of the largest crystals found in nature, sometimes reaching several meters in length. These crystals are often visually striking due to their size and clarity, making pegmatites popular among mineral collectors and geologists.
Large mineral crystals are commonly found in igneous rocks, such as granite and pegmatite, where slow cooling allows minerals to grow large. Certain metamorphic rocks, like marble and schist, can also contain large mineral crystals due to high pressures and temperatures. Veins and pockets within rocks can sometimes host large crystals as well.
Pegmatite rocks are known for having large crystals that form without a particular pattern. These rocks are often found in granite and have crystals that can be several centimeters to meters in size. The lack of clear crystal orientation in pegmatite is often due to the rapid cooling of the magma that forms them.
Orthoclase feldspar is commonly found in association with large muscovite crystals. This mineral combination is often seen in pegmatite deposits, where slow cooling allows for the growth of large crystals.
A pegmatite is an intrusive igneous rock comprised of coarse, interlocking mineral grains usually above three centimeters in diameter. Although very many pegmatites are granitic in composition, several hundred mineral species have been found in the most famous pegmatites worldwide, including many rare and valuable minerals. A few discovered pegmatite crystals have grown to several meters across.
Beryl can be found in alluvial deposits from erosion out of pegmatite veins. This is the easy way, sorting through sand and gravel. The hard way is to attack the granitic pegmatite with tools and see what's inside.
Aquamarine is a type of beryl mineral that is typically found in pegmatite rocks, rather than in soil. It forms from the crystallization of magma that cooled within these rocks over time. It is usually mined from these pegmatite deposits rather than from soil.
The mineral orthoclase is found all over the world. It can also be found in Granite rock. It would be the pink or white crystals in it.
Mineral crystal faces of varying luster and geometric shapes.
Aquamarine is a mineral that forms from the mineral beryl. Beryls can vary in age but typically form in pegmatite veins in igneous rocks. The mineral itself can be found in rocks that are hundreds of millions of years old.
Salt (NaCl) is an inorganic compound that is found in nature as solid crystals.
Quartz crystals have been found that are over 30 meters in length. For a list of the world's largest mineral crystals, click on the link below.