Sacrofanite

Chemical formula: (Na<sub>61</sub>K<sub>19</sub>Ca<sub>32</sub>)(Si<sub>84</sub>Al<sub>84</sub>O<sub>336</sub>)(S<sup>6+</sup>O<sub>4</sub>)<sub>26</sub>Cl<sub>2</sub>F<sub>6</sub>·2H<sub>2</sub>O

Sacrofanite is a very rare mineral from the tectosilicate group, distinguished by its complex chemical composition and occurrence as hexagonal crystals.

## Characteristics Sacrofanite is a complex sulfate, chloride, and fluorosilicate of sodium, potassium, and calcium, belonging to the cancrinite group. This mineral forms transparent, hexagonal crystals with a tabular or short-prismatic habit, reaching up to 2 mm. It usually occurs as single, well-formed crystals in vugs and small rock cavities. ## Physical Properties Sacrofanite crystals are characterized by a vitreous luster. They are brittle, and their Mohs hardness is approximately 5. The mineral's density is low, at 2.43 g/cm³. ## Colors and Varieties Sacrofanite is colorless. No color or commercial varieties have been identified. ## History and Name The mineral was discovered and described in 1980 by a team of mineralogists: E. Burragato, G.C. Parodi, and P.F. Zanazzi. Its name comes from the discovery location – the Sacrofano volcanic complex, situated north of Rome, Italy. It was approved by the International Mineralogical Association (IMA) in the same year. ## Uses Sacrofanite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and scientists studying the petrology of volcanic rocks.

Properties

Mohs hardness
5
Luster
Vitreous
Streak
White
Density
2.43
Cleavage
Good on {10-10}
Fracture
Conchoidal
Transparency
Transparent
Crystal system
Hexagonal

Diagnostic features

## Identification Sacrofanite can be identified by its characteristic crystal form – hexagonal, tabular, or short prismatic. Its occurrence is limited to a specific geological environment – volcanic lavas in the Lazio region of Italy. Vitreous luster and colorlessness are also helpful features. ## Distinguishing from Similar Minerals It can be confused with other colorless zeolitic minerals or feldspathoids found in the same environment, such as leucite or sanidine. Distinguishing it requires analysis of crystal form (sacrofanite is hexagonal, leucite is tetragonal with a pseudo-regular appearance) and often advanced research methods, such as X-ray diffraction (XRD). ## Crystal Forms It forms hexagonal crystals with a tabular habit, featuring well-developed basal faces {0001}, or short-prismatic. Crystals are typically small, not exceeding a few millimeters.

Geological environment

## Genesis Sacrofanite forms in the final stages of crystallization of alkali-rich, silica-poor volcanic lava. It crystallizes in cavities and vugs within volcanic rocks, such as phonolites and leucite tephrites. It is a product of pneumatolytic and hydrothermal activity associated with volcanism. ## Mineral Associations This mineral co-occurs with other rare minerals typical of this environment, such as sanidine, leucite, haüyne, biotite, pyroxene, as well as members of the cancrinite and sodalite groups. ## Localities The only confirmed and most important occurrence of sacrofanite in the world is its type locality: the quarry in Sacrofano, in the province of Rome, in the Lazio region of Italy. It is an endemic mineral to this single volcanic complex.

Rarity

Very rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with sharp, well-formed, transparent, and undamaged sacrofanite crystals, set on a contrasting rock matrix. Due to the small size of the crystals, their perfect form and clarity are crucial. Specimens with numerous crystals in a vug are more desirable than single crystals. ## Popular Localities The only source of sacrofanite specimens is its type locality in Sacrofano, Italy. All specimens available on the collector's market originate from this single location.

Care and storage

## Cleaning Sacrofanite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its brittleness and potential reactivity, washing in water, and especially using ultrasonics, should be avoided. ## What to Avoid Contact with acids and other chemicals that could damage delicate crystals should be avoided. The mineral is brittle, so it must be protected from impacts and scratching. It should not be heated or exposed to sudden temperature changes. ## Storage Due to their small size and fragility, sacrofanite specimens are best stored in enclosed "micromount" boxes, which protect them from dust, moisture, and mechanical damage. Exposure to direct sunlight should be avoided, although there is no evidence of fading.

External references

Sources

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