what kind of rocks are gemstones found in?

Answer 1

Mostly igneous rocks since it takes a lot of pressure and heat to create many of them.

The only offical gemstones are diamonds, rubies, sapphires, emeralds, andalusite, axinite, cassiterite, clinohumite and bixbite. Most of these stones can be made in lab conditions using high heat and pressure.

Amber is old tree sap.
Diamonds come from volcano fried carbon.
Rubies are made out of cooked aluminium or corundum, ruby is the red variety of the species corundum, while any other color of corundum is considered sapphire. (for red ones).
Emeralds come from the mineral beryl.

According to Wikipeida: http://en.wikipedia.org/wiki/Gemstone
"Aside from the diamond, the ruby, sapphire, emerald, pearl (strictly speaking not a gemstone) and opal [6] have also been considered to be precious. At least at the beginning of the 20th century these stones were considered precious more often than not because of their beauty. Up to the discoveries of bulk amethyst in Brazil in the 19th century, amethyst was considered a precious stone as well, going back to ancient Greece. Even in the last century certain stones such as aquamarine, peridot and cat's eye have had their days of increased popularity and hence value, much like present day.

Nowadays such a distinction is no longer made by the trade. Many gemstones are used in even the most expensive jewelry, depending on the brand name of the designer, fashion trends, market supply, treatments etc. Nevertheless, diamonds, rubies, sapphires and emeralds still have a reputation that exceeds those of other gemstones.

Rare or unusual gemstones, generally meant to include those gemstones which occur so infrequently in gem quality that they are scarcely known except to connoisseurs, include andalusite, axinite, cassiterite, clinohumite and bixbite."