Not a mineral encyclopedia but a workshop guide: for every material you will find how it formed, how to recognize it and how it can be sawn, ground, polished and drilled.
Agate
Mohs hardness 6.5 – 7The banded variety of chalcedony, grown in the gas cavities of solidified lava. Germany's best known deposit lies along the Nahe near Idar-Oberstein, another one in the Black Forest.
Amethyst
Mohs hardness 7The violet variety of quartz, colored by iron and natural radiation. Close by, near Sulzburg in the Münstertal valley, it occurs together with agate and baryte in old ore veins.
Markgräfler Bohnerz Jasper
Mohs hardness 6.5 – 7Jurassic chert stained yellow and red by the iron of the Bohnerz formation. Used for at least 27,000 years, from Stone Age blades to the Prague Kunstkammer.
Flint
Mohs hardness 6.5 – 7Formed around 70 million years ago in the Cretaceous and carried to the Baltic coast by the ice. Glassy black inside, with a white crust outside, and a popular beach find as a hag stone.
Fluorite
Mohs hardness 4Cubes in violet and green, grown from hot solutions in the veins of the basement rock. Described using the example of the Clara Mine near Oberwolfach in the Black Forest.
Rhyolite Agate
Mohs hardness 6.5 – 7Agate as a jagged star inside a ball of rhyolite, also known as a thunderegg. Described using the example of the Teufelskanzel near Oberthal in Saarland.
Petrified Wood
Mohs hardness 6.5 – 7Fossil wood whose cell structure was replaced by chalcedony and opal over millions of years. Polished sections often still show the growth rings and grain of the original tree.
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