Northupite

Chemical formula: Na₃Mg(CO₃)₂Cl

Northupite is a rare evaporite mineral from the carbonate group, forming characteristic, isometric octahedral crystals.

## Characteristics Northupite is a rare sodium magnesium halocarbonate. It occurs as well-formed, single crystals, most often adopting the form of regular octahedra. Crystals can reach several centimeters in diameter and are often embedded in the surrounding rock mass, for example, in trona or shortite. Specimens are usually opaque, less frequently translucent, with a dull or vitreous luster. ## Physical Properties This mineral is characterized by a hardness of 3.5-4 on the Mohs scale, making it relatively soft. Its density is approximately 2.38 g/cm³. It does not exhibit cleavage, and its fracture is conchoidal. It is brittle and readily dissolves in acids, releasing carbon dioxide. ## Colors and Varieties Northupite is most often colorless, white, or gray. It is sometimes yellowish or brownish due to inclusions of other minerals or organic substances. No color or commercial varieties are distinguished. ## History and Name The mineral was discovered in 1895 by C. H. Northup at Searles Lake, California, USA. Its name comes from the discoverer's surname. It was first described by W. H. Melville in 1895. ## Uses Northupite has no industrial significance. However, it is a valued and sought-after collector's mineral due to its rarity and well-formed crystals.

Properties

Mohs hardness: 3.5-4
Color: Colourless, pale yellow, grey, brown; colourless in transmitted light
Luster: Vitreous
Streak: White
Density: 0
Cleavage: None
Fracture: Conchoidal
Transparency: Transparent
Crystal system: Isometric

Diagnostic features

## Identification The most characteristic feature of northupite is its isometric, octahedral crystal form. Its low hardness and vigorous reaction with acids (effervescence) also aid identification. Occurrence in an evaporitic environment, in association with other saline minerals, is a strong diagnostic indicator. ## Distinguishing from Similar Minerals Northupite is sometimes confused with other evaporite minerals of similar habit, such as shortite, with which it often co-occurs. However, shortite crystallizes in the orthorhombic system and has different inter-facial angles. From halite (rock salt), it is distinguished by its crystal form (octahedra instead of cubes) and lack of a salty taste. ## Crystal Forms Northupite crystallizes in the isometric system, forming almost exclusively crystals with the ideal octahedral form {111}. Rarer forms are combinations of octahedron and cube. Crystals occur as single individuals embedded in the rock mass.

Geological environment

## Genesis Northupite is an evaporite mineral. It forms as a result of precipitation from highly saline, alkaline lake waters in dry and hot climates. It forms directly in bottom sediments (clays, silts) rich in carbonates and chlorides. ## Mineral Associations This mineral most often co-occurs with other evaporites, such as trona, thermonatrite, pirssonite, gaylussite, shortite, as well as halite and borax. It is often found as inclusions in trona or shortite crystals. ## Localities The most important and classic locality for northupite is Searles Lake in San Bernardino County, California, USA, where it was discovered. It is also found in other dry lakes, including Deep Spring Lake (California), in the Green River Formation (Wyoming and Utah, USA), and in salt lakes in Tanzania (Lake Natron) and Uganda (Lake Katwe).

Rarity

Rare

For collectors

## Quality Criteria The most highly valued northupite specimens are those with sharp, well-formed, and large crystals of regular, octahedral shape. Transparency is also important – translucent or transparent crystals are rarer and more desirable than opaque ones. Specimens where northupite crystals are exposed on a rock matrix or contrast with other minerals (e.g., shortite) are particularly attractive. ## Popular Localities The most classic and highly prized specimens by collectors come from Searles Lake in California and the Green River Formation in Wyoming, USA. These localities provide the largest and best-formed crystals.

Care and storage

## Cleaning Northupite specimens should only be dry-cleaned, using a soft brush to remove dust. Contact with water, even distilled water, can lead to its partial or complete dissolution. ## What to Avoid Contact with water, acids, and other chemicals must be strictly avoided. The mineral is sensitive to moisture, so it should not be stored in humid environments. It is also brittle and susceptible to mechanical damage. ## Storage It is recommended to store northupite in a dry place, preferably in a tightly sealed container (e.g., a "membrane box") or with a desiccant (silica gel). It should be protected from dust and sudden temperature changes.