Minerals, Rocks, Gemstones, Crystals.What’s the Difference?
Minerals, rocks, gemstones, crystals—unless you're a geologist or perhaps earned a merit badge studying them as a scout, explaining the differences among these four natural substances might pose a challenge.
Mineral - According to geologists, minerals are naturally occurring inorganic substances with a definite chemical composition and ordered internal structure. Examples: calcite and quartz. Rocks, crystals and gemstones are made of minerals.
Rock - Rocks are commonly composed of a mixture of different minerals, which vary in number and type depending on the rock. The most abundant minerals in Earth’s crust are amphibole, feldspar, mica, olivine, pyroxene and quartz, but some experts include other minerals such as calcite and clay minerals. A common example of a rock that is formed from two minerals is granite, which consists mainly of quartz and feldspar.
Rock versus stone – while they can used interchangeably, the Oxford English Dictionary (OED), defines rock as "A large rugged mass of hard mineral material or stone... " Examples: Plymouth Rock, Ayers Rock, The Rock of Gibraltar or a generic "large rock formation." The OED defines stone as "A piece of rock or hard mineral substance of a small or moderate size." The word "rocks" can be substituted for "stones."
Crystal - According to Walter Schumann's Gemstones of the World, a crystal is a uniform body with its smallest components (atoms, molecules, etc.) in a geometric crystal lattice. Snowflakes, diamonds and table salt are examples of large crystals. Varying lattice structures and their chemical components result in varying physical properties of the crystals . Rocks are aggregates of one or more minerals, so some rocks may have crystals in them. 
Gemstone – The definition of a gemstone is very broad. Any material that has been cut and polished to be used in jewelry or other decorative applications is a gemstone. The selection of materials for gemstones is based on criteria such as beauty, resilience, scarcity and intrinsic value. This diverse category includes over two hundred gemstones from sources ranging from minerals and crystals to semi-precious stones and even organic materials like pearls and coral.