Wolfeite

Chemical formula: Fe<sup>2+</sup><sub>2</sub>PO<sub>4</sub>(OH)

Wolfeite is a rare phosphate mineral from the triphylite group, forming brown, resinous crystals and aggregates in granitic pegmatites.

## Characteristics Wolfeite is a basic iron(II) phosphate belonging to the triphylite group. It occurs rarely, most often as embedded, granular, or massive aggregates. Well-formed crystals are sporadically found and are usually small, reaching up to 1 cm in length. They adopt a tabular or prismatic habit. This mineral is brittle. ## Physical Properties It is characterized by a hardness of 4.5-5 on the Mohs scale and a density of approximately 3.83 g/cm³. The luster is typically resinous to vitreous. Wolfeite is translucent to opaque, rarely transparent. It does not exhibit fluorescence under ultraviolet light. ## Colors and Varieties Wolfeite most often ranges in color from reddish-brown to dark brown. Greenish, grayish-green, or almost black specimens are also found. On weathered surfaces, it may be covered with a darker tarnish. No named varieties of this mineral are distinguished. ## History and Name The mineral was discovered in the Palermo No. 1 mine in North Groton, Grafton County (New Hampshire, USA). It was described in 1949 by Marie Louise Lindberg. The name honors Caleb Wetherbee Wolfe (1908-1984), a professor of mineralogy and crystallography at Boston University, who first recognized this mineral as a potentially new species. ## Uses Wolfeite has no industrial application. It is of scientific and collector's interest only, being a rare and interesting member of the phosphate group.

Properties

Mohs hardness
4.5-5
Luster
Vitreous to resinous
Streak
Pale brown
Density
3.83
Cleavage
Good on {010}, poor on {100}
Fracture
Uneven to subconchoidal
Transparency
Translucent to opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Wolfeite is recognized by its characteristic resinous luster, brown color, relatively high density, and occurrence in granitic pegmatites. It often forms granular or massive aggregates. Reaction with acids can be helpful, but it is a destructive method. ## Distinguishing from Similar Minerals Wolfeite is sometimes confused with other brown phosphates found in pegmatites, such as triphylite, arrojadite, or sarcopside. It is often distinguished from triphylite by its darker color and different crystal habit. Identification can be difficult without advanced analytical methods, such as X-ray diffraction (XRD), especially for granular specimens. ## Crystal Forms Wolfeite crystals are rare. They are usually poorly formed, short-prismatic, or thick-tabular. Most often, it occurs as irregular grains, massive aggregates, or embedded masses in the host rock.

Geological environment

## Genesis Wolfeite is a hydrothermal mineral, crystallizing in the late stages of granitic pegmatite evolution. It forms as a result of metasomatism and alteration of primary phosphates, such as triphylite-lithiophilite, under conditions of decreasing temperature. ## Mineral Associations This mineral often co-occurs with other pegmatitic phosphates. Its typical associated minerals include triphylite, graftonite, sarcopside, arrojadite, strengite, phosphosiderite, vivianite, as well as quartz, feldspars, and micas. ## Localities The most important and classic wolfeite localities are in the USA, in pegmatites of New Hampshire (Palermo No. 1, Fletcher, Valencia mines), South Dakota (Tip Top mine), and Maine. It is also known from Hagendorf-Süd in Bavaria (Germany), Finland (Viitaniemi), Brazil (Minas Gerais), and from rare occurrences in pegmatites in Rwanda.

Rarity

Rare

For collectors

## Quality Criteria Specimens with well-formed, sharp crystals are most valued by collectors, which is a great rarity for this mineral. An intense, reddish-brown color and good, resinous luster are also important. Specimens with visible crystals on matrix, especially in association with other rare phosphates, achieve higher value. Crystal size is a key factor – any crystal above a few millimeters is considered significant. ## Popular Localities Classic and most sought-after wolfeite specimens come from the type locality in New Hampshire, USA (Palermo No. 1 mine). Specimens from the Tip Top mine in South Dakota are also highly prized by collectors specializing in pegmatitic phosphates.

Care and storage

## Cleaning Wolfeite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. After wet cleaning, the specimen must be thoroughly dried. ## What to Avoid Wolfeite is sensitive to acids, which can damage it. Contact with household chemicals and cleaning agents should be avoided. As a mineral containing iron(II), it can be susceptible to oxidation, so it should be protected from moisture and high temperatures, which can accelerate this process and change its color. ## Storage Wolfeite specimens are best stored in a dry place, in closed boxes or display cases, to protect them from dust and sudden changes in humidity. It is advisable to isolate it from minerals that could scratch it (harder than 5 on the Mohs scale).

Sources

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