In the past, "cardinal" gems (diamonds, emeralds, sapphires and rubies used for royalty or religious figures) were considered more valuable than other faceted gemstones. But that has changed. There are no real differences between precious and semi-precious categories. Stones have their own qualities.
Although most people consider garnets to be only red, more than 10 types of garnets exist and they exist in many colours. Blue is the only colour the chemical composition cannot recreate. Red garnets are pyrope, almandine and rhodolite (a mixed crystal of almandine and pyrope). Radiant orange to red garnets are spessartites. The green family of garnets is called grossularite and can be found in yellow, green and brown colours. Tsavolite is also green and belongs to the grossularite group. Demantoids are the star of all green garnets.
Tourmaline is known as the "gemstone of the rainbow." Intense red tourmaline that doesn't change colour when under artificial light is rubellite, but the pink tourmalines will. Blue tourmalines are named indigolites, while yellow to browns are dravites and black ones are schorl. Green stones are known as verdelite unless chrome is part of the chemical make-up. If yes, it's called chrome tourmaline. Paraiba tourmalines are blue to blue-green while bright yellow stones are known as canary tourmalines. Some of these stones are bicolored, and still others are multicoloured.
Beryl stone consists of beryllium-aluminium-silicates, and there are many types of beryl, in many colours. Aquamarine, emerald (a cardinal stone) and morganite (peach, pink, or rose) are all beryl stone. When manganese is thrown into the mix, pink beryl is created. Golden beryl (green-yellow) is also available.
Many semiprecious gems fall into the quartz category, including purple amethyst (an original cardinal stone), citrine, ametrine (a mixed crystal of amethyst and yellow citrine), rose quartz, smoky quartz (transparent brown) and rutilated quartz (with gold "needles"). These stones are popular not only because of their good looks, but because they are affordable. Agate and chrysoprasecan are included, and can also be carved into interesting shapes. Golden brown tiger's eye and clear rock crystal are also popular.
When quartz forms not as a single crystal but as many microcrystals, it is known as chalcedony. This makes the range of chalcedonies larger than of transparent quartz, including patterned stone as well as solids. Some types of chalcedonies are agate (banded) and moss agate (patterned), bloodstone (red on green), jasper (which forms in many different colours), onyx (black), carnelian (red-brown) and chrysoprase (translucent apple green.)