Parakeldyshite

Chemical formula: Na₂Zr₄+Si₂O₇

Parakeldysite is a rare sodium zirconium silicate, forming colorless or white, prismatic crystals in nepheline syenites.

## Characteristics Parakeldysite is a sodium zirconium silicate, belonging to the group of rare minerals. It is dimorphous with keldysite, meaning it has an identical chemical composition but a different crystal structure. It typically forms small, short prismatic crystals or occurs as granular aggregates and radiating rosettes. Its crystals rarely exceed a few millimeters in size. ## Physical Properties This mineral is characterized by a hardness of 6 on the Mohs scale, making it relatively scratch-resistant. It has a vitreous luster and is transparent. Its density is quite high for a silicate, approximately 3.35 g/cm³. ## Colors and Varieties Parakeldysite is most often colorless or white. Occasionally, it may exhibit delicate yellowish or pinkish hues, likely due to trace impurities. No named color varieties or commercial forms are distinguished. ## History and Name The mineral's name refers to its relationship with keldysite – the prefix "para-" (from Greek "beside," "beyond") indicates its dimorphous nature. It was first described in 1977 by Alexander P. Khomyakov and collaborators based on material from the Khibiny Massif on the Kola Peninsula, Russia. The parent mineral, keldysite, was named in honor of Mstislav Vsevolodovich Keldysh, a Soviet mathematician and mechanic. ## Uses Due to its rarity and small crystal size, parakeldysite has no industrial applications. It is solely an object of scientific interest and a prized acquisition for advanced rare mineral collections.

Properties

Mohs hardness: 6
Luster: Vitreous
Streak: White
Density: 3.35
Cleavage: Perfect on {001} and {100}
Fracture: Uneven
Transparency: Transparent
Crystal system: Triclinic

Diagnostic features

## Identification Identifying parakeldysite in the field is difficult and relies mainly on its occurrence environment (agpaitic pegmatites) and associated minerals. In a collection, it can be recognized by its short, prismatic crystal habit, vitreous luster, and relatively high hardness (6 on the Mohs scale). Its perfect cleavage in two directions is also characteristic. ## Distinguishing from Similar Minerals Parakeldysite is visually indistinguishable from keldysite – this requires X-ray diffraction (XRD) analysis. It can be confused with other colorless or white minerals from alkaline rocks, such as nepheline, analcime, or feldspars. It is distinguished from them by its higher density, greater hardness, and specific crystal form. ## Crystal Forms It forms short, prismatic, often flattened crystals. It also occurs as granular, fibrous, or radiating rosette aggregates. Crystals are usually small, rarely exceeding a few millimeters in length.

Geological environment

## Genesis Parakeldysite is a magmatic mineral, crystallizing in the late stages in ultrabasic, alkali- and zirconium-rich rocks, known as agpaitic nepheline syenites and associated pegmatites. ## Mineral Associations It most often co-occurs with other rare minerals typical of alkaline environments, such as keldysite, eudialyte, lorenzenite, aegirine, nepheline, microcline, lamprophyllite, lomonosovite, and catapleiite. ## Localities The most important and classic localities of parakeldysite worldwide are the alkaline massifs of the Kola Peninsula in Russia (Khibiny and Lovozero), where it was discovered. It is also known from the famous Mont Saint-Hilaire locality in Quebec, Canada, and from the Ilimaussaq alkaline complex in Greenland.

Rarity

Rare

For collectors

## Quality Criteria The most valuable specimens for collectors are those with well-formed, sharp, and transparent crystals. Rich crystal aggregates and associations with other rare and aesthetic minerals, such as eudialyte or lorenzenite, are also highly prized. Crystal size is a key factor, as larger specimens are exceptionally rare. ## Popular Localities The most sought-after specimens by collectors come from the classic localities for rare minerals: the Khibiny and Lovozero massifs on the Kola Peninsula (Russia) and Mont Saint-Hilaire (Canada). Specimens from these locations are considered exemplary for this species.

Care and storage

## Cleaning Parakeldysite specimens should be cleaned very carefully, using a soft brush and distilled water. Due to its perfect cleavage, ultrasonic cleaners are not recommended, as they can cause cracking or disintegration of the crystals. ## What to Avoid The mineral is sensitive to strong acids. Avoid sudden temperature changes, which can induce internal stresses and cracks. It should not be exposed to prolonged direct sunlight, although its distinct effect on color is not known. ## Storage It is recommended to store specimens in separate, padded boxes or display cases to protect them from dust and mechanical damage. Due to its cleavage, handle it gently, avoiding impacts and pressure.

Sources

IMA Mineral List (CNMNC)