Let’s begin with a little terminology.
A mineral is a solid formation that occurs naturally in the earth. A mineral has a definite chemical composition (the types and proportions of the chemical elements) and a crystalline lattice structure (the geometry of how the atoms are arranged and bonded together), which together determine its physical properties. Minerals are made by natural processes, such as magma cooling under the earth, precipitation, and condensation.
Crystals are a subset of minerals. Crystals are minerals whose constituent atoms,
molecules, or ions are arranged in an ordered pattern extending in all three spatial dimensions (i.e., its crystal lattice or habit). The shape of the lattice determines not only which crystal system the stone belongs to, but all of its physical properties and appearance. There are seven systems or groups, including the cubic (a.k.a. isometric), tetragonal, hexagonal, trigonal, orthorhombic, monoclinic, and triclinic.
There is also an eighth group known as the amorphous group. Stones in this group have
no crystal structure. Examples include Amber, Obsidian, and Moldavite.
(Note: We’ll talk a little more about these groups on another page).
A rock is also a solid, but is a combination of one or more minerals. Rocks can be classified depending on their chemical and mineral composition, their texture, and, most importantly, the way they were formed. They can be divided among three major groups; sedimentary, metamorphic and igneous, which, in turn, can be subdivided further. An example of a commonly known rock is granite. Granite does not have a uniform structure, but is a combination of feldspar, quarts, and mica.
The primary reason I provided these definitions is because on most websites (including this one), we refer to everything as crystals. I just wanted you to know that some of the stones that crystal healers and grid workers use are actually rocks; a combination of one or more minerals, and so technically not a “crystal”.
However, since even rocks have a vibration (see the Science page), their usefulness in crystal work might still be relevant. Realize that if a rock is just a rock (no minerals/crystals), or is a conglomerate of many minerals, the vibration will be considerably lower than a pure mineral or crystal. In addition, the vibration might not be as stable as with a crystal. In light of this, I would limit working with stones other than those few known to be beneficial (think K2).