Ajordite

Ajordite is a hypothetical mineral used in mineralogy textbooks and speculative geology as an illustrative example of solid-solution behavior in silicate systems. It is described as a framework silicate with silicon-oxygen tetrahedra linked into a three-dimensional network, with aluminum and iron acting as major cations in octahedral sites and with alkali and alkaline-earth metals such as sodium, calcium, and magnesium occupying interstitial sites. The exact composition is variable, resulting in a series of end-members.

Physical properties are given as a vitreous to silky luster, color ranging from pale yellow to green, a white streak, and a Mohs hardness of about 5.5 to 6. Crystals are described as monoclinic with prismatic to tabular habit, though in practice ajordite is mainly known from microcrystalline or xenolithic forms in teaching specimens.

Occurrence and formation are hypothetical; ajordite is proposed to form in high-temperature magmatic or metamorphic environments where substantial solid-solution among alkali and earth-alkaline cations occurs. In text, it is sometimes associated with other silicates such as chromite, olivine, and serpentine, illustrating typical paragenesis for ultramafic rocks.

Etymology and history: the name ajordite derives from the fictional Ajord region used in teaching materials to demonstrate nomenclature and mineral-chemistry concepts.

The article emphasizes that no verified natural occurrence has been reported.

Significance: as a pedagogical device, ajordite helps students understand solid-solution series, cation substitution, and structure–property relationships in framework silicates.