What is the difference between a Gem, Mineral, Crystal, and Rock? Not much!
Minerals are crystalline structures that make up the rocks on our planet and generally everything inorganic.
Rocks are typically combinations of several Minerals, and are igneous, metamorphic, or sedimentary. For instance, Granite is an igneous rock composed of the Minerals Quartz, Feldspar, Mica, Hornblende, and other combinations of Minerals.
Crystals are solid objects that exhibit well defined and often pleasing geometric shapes/structures. Most crystals are Minerals, but not all of them; Opals and silica glass are not crystals because they do not have a crystalline structure.
Gemstones or gems (also called a precious or semi-precious stone, or jewel) are a piece of attractive mineral, which, when cut and polished, is used to make jewelry or other adornments. To be a gemstone, an object must display an inherent attractiveness (color, sparkle, or other optical property) and must be able to withstand the physical abuse that frequently accompanies treatment as a gem (such as faceting and cutting) or within a piece of jewelry. For instance, popular ‘precious’ gems are diamonds, ruby, emerald, and sapphire, which are Minerals (inorganic and naturally formed). However, other gems such as Lapis Lazuli (rock), amber (fossilized tree sap), Jet (a form of Coal), pearl, and coral (rock) are not Minerals due to their organic origin.