mineral
Pyrite (Limonite Pseudo-morph after Pyrite)
Iron sulfide (FeS2) transitioning to Iron oxide-hydroxide (FeO(OH)·nH2O)
Hardness: 5.0-5.5 (as limonite); color: brownish-tan to reddish-brown (originally brassy-yellow); luster: earthy to sub-metallic; crystal structure: cubic; cleavage: none; specific gravity: 2.7-4.3
- Hardness
- 5
- Color
- brownish-tan to reddish-brown (originally brassy-yellow)
- Luster
- earthy to sub-metallic
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Physical properties
Hardness: 5.0-5.5 (as limonite); color: brownish-tan to reddish-brown (originally brassy-yellow); luster: earthy to sub-metallic; crystal structure: cubic; cleavage: none; specific gravity: 2.7-4.3
Formation & geological history
Forms through the chemical weathering and oxidation of original pyrite cubes. The pyrite molecules are replaced by limonite over geological time while the original cubic shape is preserved. Commonly found in sedimentary clays or metamorphic schists.
Uses & applications
Primarily collected as geological curiosities and mineral specimens. Historically, limonite was used as a low-grade iron ore and as a pigment for ochre.
Geological facts
These are often called 'Devil's Dice' or 'Prophecy Stones' in metaphysical circles. They are perfect examples of a 'pseudomorph,' which means 'false form,' where one mineral replaces another while retaining the first mineral's external shape.
Field identification & locations
Identify by the distinct cubic geometry that contradicts its earthy, rusty appearance. Often found in weathered outcrops of shale or limestone. Collectors look for sharp edges and lack of damage to the corners of the cube.
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