Smythite

Chemical formula: (Fe<sup>2+</sup>,Fe<sup>3+</sup>,Ni)<sub>3-3.3</sub>S<sub>4</sub>

Smythite is a rare, strongly magnetic iron and nickel sulfide, forming characteristic, thin hexagonal plates with a metallic luster.

## Characteristics Smythite is a rare sulfide mineral, chemically classified as an iron and nickel sulfide. Its most characteristic visual feature is thin, hexagonal crystals in the form of plates or flakes. They usually occur as small, individual platelets, rosette-like aggregates, or as tiny scales in rock fissures. The mineral is black, often with a brownish or bronze hue, and exhibits a strong, metallic luster. One of its key physical properties is strong magnetism. ## Physical Properties Smythite's hardness on the Mohs scale is approximately 4.5, placing it in the medium hardness range. It is opaque, and its density ranges from 4.07 to 4.3 g/cm³. It possesses perfect cleavage in one plane, parallel to the base of the hexagonal crystals, which allows it to easily split into thin plates. ## Colors and Varieties This mineral is uniformly black, sometimes with a brown or brassy tint on fresh surfaces. It does not form color varieties or commercial types. ## History and Name Smythite was first described in 1957 by Richard C. Erd, Howard T. Evans Jr., and Donald H. Richter. The mineral is named in honor of Charles Henry Smyth Jr. (1866–1937), a professor of geology and mineralogy at Princeton University, for his contributions to ore deposit research. ## Uses Due to its rarity and small crystal size, smythite has no industrial applications. It is solely an object of scientific interest and a prized acquisition for advanced mineral collections.

Properties

Mohs hardness
4.5
Luster
Metallic
Streak
Black
Density
4.07-4.3
Cleavage
Perfect on {0001}
Fracture
Uneven
Transparency
Opaque
Crystal system
Trigonal

Diagnostic features

## Identification Key diagnostic features of smythite are its form – thin, hexagonal plates – combined with its black color, metallic luster, and, most importantly, strong magnetism. Perfect cleavage in one direction, causing thin platelets to separate, is also very characteristic. ## Distinguishing from Similar Minerals Smythite is sometimes confused with other platy or magnetic minerals: - **Pyrrhotite:** Often co-occurs with smythite, but usually has a bronze-brown color and is less magnetic. - **Graphite:** Graphite has a similar appearance and habit, but is much softer (hardness 1-2), feels greasy to the touch, and is not magnetic. - **Molybdenite:** Forms similar hexagonal plates, but is very soft (hardness 1-1.5), has a slightly bluish tint, and does not exhibit magnetism. ## Crystal Forms Smythite crystallizes as thin to thick tabular crystals with a hexagonal outline. It often forms aggregates resembling rosettes, fans, or occurs as fine-grained coatings and efflorescences.

Geological environment

## Genesis Smythite is a mineral of low-temperature hydrothermal processes. It forms in voids and fissures of carbonate rocks (limestones, dolomites), as well as in serpentinites. It can also form as an alteration product of pyrrhotite in certain types of sulfide deposits. ## Mineral Associations It most commonly co-occurs with minerals such as pyrrhotite, pyrite, marcasite, calcite, dolomite, ankerite, and siderite. ## Localities Important and classic smythite localities include: - United States – geodes in limestones in Monroe County, Indiana (type locality). - Japan – Kamaishi Mine in Iwate Prefecture, where well-formed crystals were found. - Canada – Sudbury area in Ontario. - Other documented occurrences are in Germany, Austria, and Slovenia.

Rarity

Very rare

For collectors

## Quality Criteria The collector's value of smythite specimens primarily depends on the quality and size of the crystals. Specimens with sharply defined, distinct hexagonal plates are most prized, especially if they form aesthetic rosettes. A contrasting matrix, such as white calcite or dolomite, which highlights the black, metallic crystals, is also very important. Due to the mineral's rarity, even microscopic but well-formed crystals are sought after by specialists. ## Popular Localities Specimens from geodes found in limestones in Indiana (USA) are considered classic and most desirable. Well-formed crystals from the Kamaishi mine in Japan are also highly valued.

Care and storage

## Cleaning Smythite specimens should only be dry-cleaned, using a soft brush to remove dust. As a sulfide, it is sensitive to moisture and chemicals, so contact with water, and especially acids, should be avoided. ## What to Avoid This mineral is susceptible to oxidation in humid environments, which can lead to its slow decomposition and tarnishing. It should be protected from moisture, direct sunlight, sudden temperature changes, and all chemical agents. ## Storage It is recommended to store smythite in a dry and stable environment. The best solution is a sealed display box with a desiccant (e.g., silica gel). Due to the possibility of oxidation, it is advisable to isolate it from other minerals that could be damaged by contact with its decomposition products.

Sources

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