Oxy-schorl

Chemical formula: Na(Fe₂+₂Al)Al₆Si₆O₁₈(BO₃)₃(OH)₃O

Oxy-schorl is a rare mineral from the tourmaline group, distinguished by its black color and occurrence as radial aggregates or columnar crystals.

## Characteristics Oxy-schorl is a mineral belonging to the tourmaline group, approved as a distinct mineral species in 2011. It is the oxygen analogue of schorl. It forms black, opaque crystals with a columnar or acicular habit, often terminated by a trigonal pyramid. These crystals frequently exhibit longitudinal striations on their faces. It also occurs in the form of radial, rosette-like, or fibrous aggregates. ## Physical Properties It is characterized by a hardness of 7 on the Mohs scale, which is typical for tourmalines. It has a vitreous luster and is brittle, with an uneven to conchoidal fracture. The mineral's density is approximately 3.23 g/cm³. ## Colors and Varieties Oxy-schorl is a mineral of uniform, black color. No color or commercial varieties are distinguished. ## History and Name The name "oxy-schorl" refers to its chemical composition – it is the oxygen-bearing (oxy) equivalent of schorl, to which it is closely related. It was described based on material from the type locality in Zlatá Idka, Slovakia, and from Přibyslavice, Czech Republic. It was approved as a new mineral by the International Mineralogical Association (IMA) in 2011. ## Applications Due to its rarity and generally small crystal sizes, oxy-schorl is primarily a mineral of scientific and collector's interest. It has no industrial applications.

Properties

Mohs hardness: 7
Luster: Vitreous
Streak: Gray
Density: 3.23
Cleavage: None
Fracture: Uneven to conchoidal
Transparency: Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Oxy-schorl is difficult to distinguish from other black tourmalines, especially schorl, without advanced chemical (e.g., EDS, WDS) or spectroscopic analyses. Its characteristic columnar habit with vertical striations, trigonal cross-section of crystals, and black color are typical for the entire group. Hardness (7) and vitreous luster are also auxiliary features. ## Distinction from Similar Minerals Macroscopically, it is practically impossible to distinguish from schorl and dravite. Schorl is its ferrous (Fe²⁺) analogue, and dravite is its magnesian analogue. Certain identification requires chemical analysis to determine the dominant ions in specific structural positions. From other black, columnar minerals, such as hornblende, it is distinguished by greater hardness and the absence of typical amphibole cleavage. ## Crystal Forms Most often, it forms elongated, columnar crystals with a characteristic rounded triangular cross-section. The prism faces are usually strongly striated along the c-axis. It also occurs as acicular or fibrous aggregates with a radial structure.

Geological environment

## Genesis Oxy-schorl forms in granitic pegmatites and in some metamorphic rocks, such as gneisses and mica schists. Its crystallization is associated with boron-rich hydrothermal processes. ## Mineral Associations It co-occurs with minerals typical of pegmatites and metamorphic rocks, such as quartz, feldspars (especially albite), micas (muscovite, lepidolite), and also with other tourmalines, such as elbaite or dravite. ## Localities The most important confirmed occurrences of oxy-schorl are the type localities: Zlatá Idka in Slovakia and Přibyslavice in the Czech Republic. It has also been identified in other locations worldwide, including pegmatites in Maine (USA), Norway, Italy, and Russia.

Rarity

Very rare

For collectors

## Quality Criteria The most valued by collectors are well-formed, single crystals with distinct luster and smooth, striated faces. Specimens showing radial aggregates on a rock matrix, e.g., on quartz or feldspar, are also attractive. Crystal size is of great importance – larger, well-formed specimens are much rarer and more desirable. ## Popular Localities Specimens from type localities (Zlatá Idka, Slovakia; Přibyslavice, Czech Republic) hold particular value for collectors specializing in mineral systematics. Other localities providing material of collector's significance include some pegmatites in Norway and the USA.

Care and storage

## Cleaning Oxy-schorl specimens can be cleaned with lukewarm water and a mild soap, using a soft brush. Ultrasonic cleaners should be avoided, as they can cause fractures in brittle crystals. After washing, it should be thoroughly rinsed with distilled water and left to dry completely. ## What to Avoid The mineral should be protected from contact with strong acids and bases. As a member of the tourmaline group, it can be sensitive to sudden and extreme temperature changes, which may lead to internal fracturing. Prolonged exposure to intense sunlight is not recommended. ## Storage Oxy-schorl is relatively hard but brittle. It is best stored in individual display boxes or on a soft surface to prevent scratches and chipping. Protect from dust and moisture.

Sources

IMA Mineral List (CNMNC)