Fowlerite

Chemical formula: (Mn₂+,Zn₂+)SiO₃

Fowlerite is a zinc-rich variety of rhodonite, characterized by its brownish-red color and origin from the Franklin mine in the USA.

## Characteristics Fowlerite is a zinc-rich variety of rhodonite, belonging to the silicate group. Its name refers to specific, zinc-bearing specimens originating mainly from the historic locality in New Jersey, USA. Typical specimens form coarse-grained, massive aggregates or well-formed, tabular crystals often with rounded edges. Characteristic of fowlerite is its brownish-red, pinkish-brown, or reddish color, distinguishing it from typical pink rhodonite. ## Physical Properties The hardness of fowlerite on the Mohs scale is 5.5-6.5, making it a relatively hard mineral. It has a vitreous luster, and on cleavage surfaces, it can be pearly. It is transparent to translucent. The density ranges from 3.5-3.7 g/cm³, which is typical for rhodonite, though it may be slightly higher due to its zinc content. ## Colors and Varieties The dominant color is brownish-red, but specimens in shades of pink, red, and brown are also found. The presence of zinc is a key factor influencing its specific color. Fowlerite itself is a variety of rhodonite and does not form further named sub-varieties. ## History and Name The mineral was named in 1832 by Charles Upham Shepard in honor of Dr. Samuel Fowler (1779-1844), an American physician, congressman, and owner of the Franklin mine in New Jersey, from where the best specimens of this mineral originate. The name honors his contribution to the study of the mineralogy of this unique deposit. ## Applications Fowlerite is primarily a prized collector's stone, sought after for its classic origin, unique color, and well-formed crystals. It has no significant industrial application. Exceptionally massive, attractively colored fragments may occasionally be cut into cabochons.

Properties

Mohs hardness: 5.5-6.5
Luster: Vitreous to pearly
Streak: White
Density: 3.5-3.7
Cleavage: Perfect on {110} and {1-10}
Fracture: Conchoidal to uneven
Transparency: Transparent to translucent
Crystal system: Triclinic

Diagnostic features

## Identification The key diagnostic features of fowlerite are its brownish-red color, vitreous luster, and the presence of two directions of perfect cleavage intersecting at an angle close to 90 degrees. Hardness (scratches glass) and relatively high density are also helpful. For specimens from Franklin, a weak, reddish fluorescence under ultraviolet light (shortwave) is characteristic. ## Distinguishing from Similar Minerals - **Rhodonite**: Fowlerite is a variety of rhodonite. It is distinguished by a higher zinc content (confirmable by chemical analysis), often a more brownish hue, and specific origin. In collecting practice, brownish specimens from Franklin are customarily called fowlerite. - **Rhodochrosite**: It is significantly softer (hardness 3.5-4), has perfect rhombohedral cleavage (three directions), and reacts vigorously with hydrochloric acid. - **Pyroxmangite**: It is a polymorph of rhodonite with a very similar appearance and properties. Definitive distinction requires specialized crystallographic studies. ## Crystal Forms Fowlerite most often forms thick, tabular crystals, often of considerable size. It also occurs as granular or massive aggregates, where distinct cleavage planes are visible.

Geological environment

## Genesis Fowlerite forms under conditions of regional or contact metamorphism in zinc and manganese ore deposits. The classic environment for its occurrence is metamorphosed, stratiform oxide-silicate deposits, such as those in the Franklin and Sterling Hill areas in the USA. ## Mineral Associations This mineral almost always occurs in association with other minerals typical of the Franklin deposit. Its most common associations include franklinite (black, metallic octahedra), willemite (often green and strongly fluorescent), zincite (red grains), and calcite (often red-fluorescent). ## Localities The most important and historic locality from which type specimens of fowlerite originate is the Franklin mine in Sussex County, New Jersey, USA. Significant quantities were also found in the nearby Sterling Hill mine. Occurrences of zincian rhodonite have also been reported in Broken Hill, Australia, but specimens from the USA are considered classic fowlerite.

Rarity

Not very common

For collectors

## Quality Criteria The most highly valued specimens are those with sharply terminated, well-formed crystals of intense, brownish-red color. Large, single crystals or aesthetic groups on a rock matrix fetch high prices. Compositions with other contrasting minerals from Franklin, such as green willemite or black franklinite, are particularly sought after. ## Popular Localities Specimens from the two historic mines in New Jersey, USA: Franklin and Sterling Hill, are considered the best in the world and most desired by collectors. These localities defined fowlerite as a unique collector's variety.

Care and storage

## Cleaning Fowlerite specimens can be cleaned with a soft brush and lukewarm, preferably distilled, water. Strong detergents should be avoided. Due to its perfect cleavage, ultrasonic cleaners are not recommended, as they can cause fracturing along cleavage planes. ## What to Avoid The mineral is sensitive to sudden temperature changes and mechanical impacts, which can lead to damage. It should be protected from contact with acids and strong chemicals. Prolonged exposure to direct sunlight is not advisable. ## Storage It is recommended to store specimens in separate, padded boxes or display cases to avoid scratches from harder minerals (e.g., quartz) and mechanical damage. Stable conditions without high humidity and temperature fluctuations should be ensured.

External references

https://en.wikipedia.org/wiki/https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FRhodonite