The Firefly Guide to Minerals, Rocks and Gems

The Firefly Guide to Minerals, Rocks and Gems

What rock is this?

This question arises time and again, whether you pick up a pebble during a walk, find a crystal in the mountains, discover golden or shining silver fragments in the waste rock piles of an ore mine, stumble over a curbstone, or when you look at a beautiful piece of jewelry. Inevitably, you will want to know: What mineral is this? What rock do I have in front of me? What is this colorful gemstone that sparkles so beautifully?

This book will help to answer these questions — as your constant companion on hikes or trips, while mountaineering or collecting minerals, in quarries and at waste rock piles, at mineral shows and also at jewelers.

With the exception of native mercury, minerals are always solid. No matter how good mineral water tastes, no matter how many minerals the label indicates, it is liquid and, therefore, not a mineral. Anything man-made, from window glass to quartz crystal in watches to artificial diamonds, is not a mineral. Pyromorphite crystals with curved prism surfaces are known as “Emser Barrels.” A mineral must always be a naturally occurring substance.

The concept of a crystal is somewhat different. Crystals are solid chemical substances whose atoms are arranged in a uniform and ordered structure. This ordered arrangement of atoms is reflected in the flat, regular surfaces which form the boundaries of a crystal. Almost all minerals are crystals, even if it is sometimes not externally apparent. There are only a few minerals whose atoms are not structurally arranged in the form of a crystal lattice — these are called amorphous. The best-known example is opal, which, in contrast to quartz (which is composed almost in the same way), cannot form crystals.

Gemstones are minerals that are cut for jewelry purposes. In order to be considered a gemstone, a mineral must meet various requirements, but primarily, it must be beautiful, i.e. satisfy aesthetic requirements. This means that it should be beautifully colored and should shine and sparkle as much as possible when polished. The latter is even more important if the mineral, such as a diamond, is normally colorless.

Rocks can be described as large geological formations that are composed of individual fragments of one or more different mineral types. Marble, for example, is made up of many grains of a single mineral: calcite. Granite, on the other hand, is composed of three mineral types: feldspar, quartz and mica.