sedimentary

Dendritic Limestone

Calcite with Manganese Oxide (Manganese Dendrites)

AI-generated identification · may be incorrect

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

Identified April 28, 2026More sedimentary →

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Physical properties

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.