Almond stone (rock)
Almond stone (amygdaloid) is a structural form of various volcanic rocks, the original cavities (bubble spaces) of which are completely or partially filled by minerals ( quartz , opal , calcite , zeolites , also green earth , alone or the filling minerals delimiting the rock) .
Often the filling masses ( almonds ) loosen easily from the rock envelope, they are often firmly attached to them and are intimately connected to it by a transition zone. Sometimes they are round, sometimes elongated or flattened, lenticular, especially often almond-like (hence the name), sometimes pear-shaped or irregular. They are also often hollow and lined with crystals on the inside . Around the core, especially in the case of quartz filling, there are numerous concentric layers of differently colored chalcedony ( agate ); often the entire filling consists of agate. The chalcedony almonds ( water stones, enhydros, more correctly: enhygros), which contain an aqueous solution and air, are of particular interest because the liquid content can be reduced by lying in dry air and increased by immersion in water. If this behavior indicates a kind of endosmosis or a communication of the almond contents with the environment through the already solidified covering by means of cracks and tubes of hair, then other almonds appear through infiltration from one point, which on sharpened specimens by bending the concentric ones Lagen can be proven to be educated. In any case, the cavities were already present, whether they were caused by gas bubbles that enclosed a solidifying mass, or by subsequent washing out of slightly weathered silicates or lime and the like. Like. Be formed. Almond stone structure is mainly found in basaltic rocks, in melaphyres and palatinites (very often), in diabase, etc. The almonds of the palatinite of the near area (Oberstein) and now, after exhaustion, those from similar South American rocks provide the agates.
