Pegmatite is a rock well known for its impressively large minerals.
It is a rock that is called so because
it has got
large minerals - whatever its composition. It is any rock with
large mineral crystals.
The minerals generally need to be larger than 3cm, however most often
they are much larger - up to 14 meters long minerals have been found in
It can be any rock such as igneous gabbro
and diorite, or
schist or gneiss,
and many others.
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Most often, however, it is a rock
related to granite
(they are called granitoids), and so most often it
contains minerals such as quartz,
and mica such as
other cases, some impressive minerals found in this rock have been
spodumene, tourmaline, beryl, garnet, topaz, and some rare
elements such as tungsten, tin, gallium, rubidium, beryllium
The reason for the large
minerals is that this rock forms in the last
stages of the formation of an intrusion, where water is involved.
makes it possible for the crystals to grow so large because it makes
all the particles very mobile.
While large crystals normally only form
when the cooling is very slow, over millions of years, in pegmatites
they can form much quicker and still grow very large.