sedimentary
Dendritic Limestone
Calcite with Manganese Oxide (Manganese Dendrites)
Hardness: 3 (substrate) / 5.5-6 (dendrites); Color: Buff, tan, or white base with black or dark brown fern-like patterns; Luster: Dull or earthy; Crystal structure: Trigonal (calcite matrix) / Amorphous or dendritic growth (manganese oxides).
- Hardness
- 3 (substrate) / 5
- Luster
- Dull or earthy
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Physical properties
Hardness: 3 (substrate) / 5.5-6 (dendrites); Color: Buff, tan, or white base with black or dark brown fern-like patterns; Luster: Dull or earthy; Crystal structure: Trigonal (calcite matrix) / Amorphous or dendritic growth (manganese oxides).
Formation & geological history
Formed when manganese-rich mineral-bearing solutions percolate through tiny cracks or bedding planes in sedimentary rocks like limestone or siltstone. As the water evaporates, manganese oxides precipitate in branching, tree-like patterns known as 'pseudofossils'.
Uses & applications
Primarily used as decorative display specimens, paperweights, or in lapidary work for jewelry cabochons. It is also used as an ornamental stone in architecture.
Geological facts
Manganese dendrites are often mistaken for fossilized plants or moss (pseudofossils), but they are actually inorganic crystal growths. They grow in a fractal pattern similar to frost on a window.
Field identification & locations
Identify in the field by looking for black, delicate, branching 'ferns' on the surface of sedimentary bedding planes. Unlike real fossils, they do not have organic structure and often cross over biological features.
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