Quartz is the most common mineral on Earth. Its share in the earth's crust is about 60%. Quartz is used in industry, in jewelry, especially rare and interesting specimens are acquired for collections.

Quartz has many varieties, but first it is worth considering the two main groups of this mineral - crystalline and cryptocrystalline. The first is formed in the earth's crust in the form of crystals, the second, respectively, does not have crystals. The photo below shows an example of how cryptocrystalline quartz (striped agate) turns into crystalline (amethyst, rauchtopaz, rock crystal).

Among the quartz that form crystals, one can name citrine, morion, rauchtopaz, amethyst, rock crystal. Interestingly, the colors in this group of quartz are unstable, and one type of quartz is easily transformed into another by heating or irradiation - amethyst and morion into citrine, amethyst into green prasiolite, and each of the quartz that has a color into rock crystal, since when heated up to a certain temperature, they completely lose their color.
It is also necessary to note another group of crystalline quartz - "hairy" quartz. "Hairs" are crystals of rock crystal (clear quartz) with needle-like inclusions of rutile ("Venus hair") or tourmaline ("Cupid's arrows"). Here one should be careful in the name of the corresponding stone, since rock crystal with rutile inclusions is often called rutile quartz, simply shortened to "rutile", which is incorrect, since rutile is only one of the parts that make up rutile quartz. Moreover, the short, but categorically incorrect designation "rutile" can also refer to quartz with inclusions of black tourmaline (the so-called "black hairy").

It is interesting that, since inclusions in quartz are very common, they have their own names not only "hairy", but also, for example, quartz with multiple inclusions of chlorite - they are called lodolites or aquarium quartz in another way. Quartz with inclusions of hematite and lepidocrocyte is called strawberry quartz.
It also sometimes happens that different types of inclusions can be found in one stone. Below is a sample of quartz with inclusions of rutile and other minerals.

Cryptocrystalline quartz is even more interesting - it has more varieties, as well as optical effects. For example, agates and rose quartz can have opalescence, while rose quartz can have an asterism effect. It is interesting that rose quartz owes this optical effect to the inclusion of the finest hairs of rutile, which, being distributed in a special way, create a distribution of the light flux over the stone so that we see a star.
It should be noted here that rose quartz sometimes still forms crystals, but this is quite rare, and therefore it is referred mainly to cryptocrystalline quartz.

Despite the fact that quartz is obtained artificially on an industrial scale, grown quartz is rare in the jewelry market. There are two reasons for this. The first is that quartz is a relatively inexpensive stone, and the cost of grown quartz is approximately equal to the cost of natural. The second - quartz attracts us with its features, imperfections, inclusions and optical effects, while quartz is artificially grown only in order to obtain more "ideal" chemically pure samples. This is good for industrial use, but in the jewelry business, these specimens are hardly in demand.