Morinite

Chemical formula: NaCa<sub>2</sub>Al<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>(OH)F<sub>4</sub>·2H<sub>2</sub>O

Morinite is a rare phosphate mineral found in granitic pegmatites, forming small, vitreous crystals and radial aggregates.

## Characteristics Morinite is a hydrated sodium, calcium, and aluminum phosphate with additional fluoride and hydroxyl anions. It most commonly occurs as aggregates of small, prismatic or acicular crystals, which often form radial, spherulitic, or fan-shaped habits. Individual, well-formed crystals are rare and typically small, usually not exceeding a few millimeters. The mineral is brittle. ## Physical Properties Morinite crystals are characterized by a vitreous luster. Its Mohs hardness is approximately 4, and its density ranges from 2.94 to 3.0 g/cm³. It is transparent to translucent. It does not exhibit fluorescence under ultraviolet light. ## Colors and Varieties Morinite is usually colorless or white. It can also take on pink, yellowish, or light brown hues, likely due to the presence of impurities. No named varieties of this mineral are distinguished. ## History and Name The mineral was first described in 1891 by Alfred Lacroix. Its name comes from the Morini (or La Vilatte) mine in the Creuse department, France, which is its type locality. The mine's name, in turn, refers to the Morini, a Gallic tribe that once inhabited northern France. ## Uses Morinite has no industrial applications. Its significance is purely scientific and as a collector's item.

Properties

Mohs hardness
4
Luster
Vitreous
Streak
White
Density
2.94-3.0
Cleavage
Good on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Characteristic features of morinite include its habits – radial or fan-shaped aggregates of small, acicular crystals with a vitreous luster. Its occurrence in granitic pegmatites, associated with other phosphates, is also an important diagnostic clue. It reacts with acids. ## Distinguishing from Similar Minerals Radial aggregates of morinite can resemble some zeolites (e.g., natrolite, mesolite) or other phosphates, such as wavellite. It differs from wavellite by its lower hardness and different occurrence environment (wavellite more often forms in weathering zones of sedimentary rocks). It can be distinguished from zeolites based on chemical tests and associated minerals. ## Crystal Forms Morinite crystallizes in the monoclinic system. It forms elongated, prismatic or acicular crystals, often terminated by sloping faces. It is most commonly found in radial, fan-shaped, or spherulitic aggregates.

Geological environment

## Genesis Morinite is a secondary mineral, forming in the late stages of crystallization of granitic pegmatites. It forms as a result of hydrothermal processes or through the alteration of previously crystallized primary phosphates, such as triplite or lithiophilite, under the influence of fluorine- and sodium-rich solutions. ## Mineral Associations This mineral often co-occurs with other pegmatitic phosphates. Its typical associated minerals include: wardite, wavellite, strengite, rockbridgeite, lithiophilite, eosphorite, apatite, as well as quartz, feldspars (especially albite), and muscovite. ## Localities Key morinite localities worldwide include its type locality in Montebras, France; the Palermo No. 1 mine in New Hampshire and mines in the Custer and Keystone areas in South Dakota, USA; and pegmatites in Hagendorf-Süd in Bavaria, Germany. It is also found in Brazil (Minas Gerais) and Rwanda.

Rarity

Rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with well-formed, sharply terminated crystals, forming aesthetic, radial or fan-shaped groups. Transparent crystals with distinct luster and attractive color (e.g., pink) are desirable. A contrasting association with matrix minerals or other phosphates (e.g., dark rockbridgeite) significantly enhances the visual and collector's value of the specimen. ## Popular Localities Classic and prized specimens come from localities in the USA, especially from the Palermo No. 1 mine in New Hampshire, where relatively large and well-formed aggregates have been found. The German locality Hagendorf-Süd has also yielded many high-quality micromineralogical specimens.

Care and storage

## Cleaning Morinite specimens should be cleaned very carefully, using a soft brush to remove dust. Brief rinsing in distilled water is permissible, followed by thorough drying. Due to its brittleness, ultrasonic cleaners and mechanical cleaning should be avoided. ## What to Avoid The mineral is sensitive to acids, which can damage it. Contact with household and laboratory chemicals should be avoided. It should not be heated or exposed to sudden temperature changes. ## Storage Collector's specimens of morinite, due to their delicacy and small size, are best stored in sealed "micromount" boxes, which protect them from dust and mechanical damage. Storage in humid conditions should be avoided.

Sources

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