Homilite

Chemical formula: Ca₂Fe₂+B₂(SiO₄)₂O₂

Homilite is a rare calcium iron borosilicate, forming brown or black, resinous crystals, prized by collectors of rare minerals.

## Characteristics Homilite is a complex borosilicate belonging to the datolite group. Its name comes from the Greek word meaning "to occur together," referring to its frequent association with meliphanite and other rare minerals. It typically forms short, prismatic or tabular crystals, often with an almost square cross-section. Specimens are rarely transparent, most often being translucent or nearly opaque. Crystal surfaces can be smooth and shiny, but are often corroded or covered with coatings. ## Physical Properties This mineral is characterized by a hardness in the range of 5.5 on the Mohs scale, making it relatively scratch-resistant. Its luster is distinctly resinous, and on fracture surfaces, it can be greasy. The density of homilite is approximately 3.26-3.37 g/cm³, making it noticeably heavier than most common silicates, such as quartz. ## Colors and Varieties Homilite occurs in a limited color range. Specimens ranging from brown to black are most commonly found. Occasionally, brownish-red or brownish-yellow hues appear. No named varieties of this mineral are distinguished. ## History and Name The mineral was first described in 1876 by the Swedish chemist and mineralogist Christian Wilhelm Blom. The name, given by S. R. Paijkull, comes from the Greek "ὁμιλεῖν" (homilein) - "to occur together," referring to its discovery in association with meliphanite and erdmannite on the island of Stokkøya in Norway, which is its type locality. ## Uses Homilite has no industrial applications. It is a mineral of purely scientific and collectible interest, sought after for its rarity and classic occurrences.

Properties

Mohs hardness: 5.5
Luster: Vitreous to resinous
Streak: Grayish-white
Density: 3.26-3.37
Cleavage: Indistinct on {110}
Fracture: Uneven to sub-conchoidal
Transparency: Translucent to opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Homilite is identified by its characteristic, strongly resinous luster, brown to black color, relatively high density, and crystal habit. Crystals are usually short, prismatic, often with an almost square outline. Occurrence in a specific geological environment, such as nepheline syenites and pegmatites, is also an important clue. ## Distinguishing from Similar Minerals Homilite can be confused with other dark pegmatitic minerals. It differs from black tourmaline (schorl) by its lower hardness and different crystal habit (tourmaline has a trigonal cross-section). It differs from garnets (e.g., andradite) by its irregular fracture (garnets have conchoidal) and monoclinic crystal system. Examination of associated minerals is also helpful in identification. ## Crystal Forms Homilite crystals crystallize in the monoclinic system but often exhibit pseudo-tetragonal symmetry. They usually form short, thick prisms or tabular crystals. They can occur as single, well-formed crystals embedded in the host rock or as irregular granular aggregates.

Geological environment

## Genesis Homilite is an igneous mineral, crystallizing in the late stages from alkaline, silica-poor magmas. It forms mainly in syenite pegmatites and nepheline syenites, where rare elements such as boron are concentrated. ## Mineral Associations This mineral often co-occurs with other rare minerals typical of alkaline pegmatites. Its most common associations include: meliphanite, aegirine, albite, microcline, nepheline, zircon, titanite, magnetite, and pyrochlore. ## Localities The most important and classic homilite localities are in Norway, in the Langesundsfjorden area (e.g., on the islands of Stokkøya and Låven), from which the best-formed crystals originate. It is also known from rare occurrences in Mont Saint-Hilaire in Quebec (Canada) and from several localities in Russia on the Kola Peninsula (Khibiny and Lovozero massifs).

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with sharply terminated, well-formed, single crystals with a strong, resinous luster. Crystals contrastingly set on a light rock matrix, such as white albite or microcline, are also highly valued. Size matters – crystals exceeding 1-2 cm are already considered large and rare. Transparency, though rare, significantly increases the specimen's value. ## Popular Localities Undoubtedly, the most sought-after homilite specimens come from the classic localities in Norway, in the Langesundsfjorden area. Material from these localities is considered exemplary for this species. Specimens from Mont Saint-Hilaire in Canada are also valued, although they often have a slightly different appearance.

Care and storage

## Cleaning Homilite specimens should be cleaned very carefully. It is best to use a soft brush to remove dust. If necessary, compressed air can be used. If wet cleaning is required, distilled water and a soft brush are recommended, followed by thorough drying of the specimen. Ultrasonic cleaners should be avoided. ## What to Avoid Homilite is sensitive to strong acids, which can damage it. Contact with household and laboratory chemicals should be avoided. The mineral is stable, but extreme thermal shocks should be avoided. Prolonged exposure to direct sunlight is not recommended, although there is no evidence of fading. ## Storage Homilite specimens, especially those with well-formed crystals, should be stored in separate, padded boxes to prevent scratches and chipping from harder minerals. It is best to display them in enclosed showcases, protecting them from dust and sudden temperature changes.

External references

https://en.wikipedia.org/wiki/https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FHomilite