Rocks, Minerals, Crsytal Guide 4+

What are Rocks
A rock is a solid mass of geological materials. Geological materials include individual mineral crystals, inorganic non-mineral solids like glass, pieces broken from other rocks, and even fossils. The geological materials in rocks may be inorganic, but they can also include organic materials such as the partially decomposed plant matter preserved in coal. A rock can be composed of only one type of geological material or mineral, but many are composed of several types.

Rocks are grouped into three main categories based on how they form. Igneous rocks form when melted rock cools and solidifies. Sedimentary rocks form when fragments of other rocks are buried, compressed, and cemented together; or when minerals precipitate from solution, either directly or with the help of an organism. Metamorphic rocks form when heat and pressure alter a pre-existing rock. Although temperatures can be very high, metamorphism does not involve melting of the rock.

A rock is any naturally occurring hard solid mass. In terms of composition it is an aggregate of minerals. For example granite rock composed of quartz, feldspar and mica etc.

What are Minerals
A mineral is an element or chemical compound that is normally crystalline and that has been formed as a result of geological processes. Examples include quartz, feldspar minerals, calcite, sulfur and the clay minerals such as kaolinite and smectite.

Minerals are naturally occurring elements or compounds. Most are inorganic solids (apart from liquid mercury and a few organic minerals) and defined by their chemical composition and crystal structure.

Minerals can be readily identified by several physical properties such as hardness, lustre, streak and cleavage. For example, the mineral talc is very soft and easily scratched whereas the mineral quartz is quite hard and not so easily scratched.

Crystals
crystal, any solid material in which the component atoms are arranged in a definite pattern and whose surface regularity reflects its internal symmetry.
All minerals form in one of seven crystal systems: isometric, tetragonal, orthorhombic, monoclinic, triclinic, hexagonal, and trigonal. Each is distinguished by the geometric parameters of its unit cell, the arrangement of atoms repeated throughout the solid to form the crystal object we can see and feel.

What all crystals have in common is an extremely well-organized molecular structure. In a crystal, all of the atoms (or ions) are arranged in a regular grid pattern. For example, in the case of table salt (NaCl), the crystals are made up of cubes of sodium (Na) ions and chlorine (Cl) ions. Each sodium ion is surrounded by six chlorine ions. Each chlorine ion is surrounded by six sodium ions. It's very repetitive, which is exactly what makes it a crystal!

Gemstones
A gemstone (also called a fine gem, jewel, precious stone, semiprecious stone, or simply gem) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments.

Gemstones are minerals, rocks, or organic matters that have been chosen for their beauty, durability, and rarity and then cut or faceted and polished to make jewelry or other human adornments. Even though most gemstones are hard, some are too soft or fragile to be used in jewelry, so they are often exhibited in museums and sought by collectors.

Gemstones Color
Gemstones are diverse in their beauty, and many are available in a stunning variety of shades and colors. Most gemstones have little beauty in the rough state, they may look like ordinary rocks or pebbles, but after a skilled cutting and polishing the full color and luster can be seen.