Indicolite
Chemical formula: A(D₃)G₆(T₆O₁₈)(BO₃)₃X₃Z
Indicolite is a blue variety of tourmaline, valued for its intense, sapphire-like colors, ranging from light blue to dark navy.
Description
## Characteristics Indicolite is a blue variety of tourmaline, a mineral from the silicate group, characterized by a richness of blue hues. The color of indicolite can range from a light, almost aquamarine blue, through intense sapphire, to dark navy, often with greenish or violet tones. Indicolite crystals typically have an elongated, prismatic habit, often with distinct striations along the c-axis. They occur as single crystals, as well as in radial or granular aggregates. Its transparency and intense color make it a highly sought-after mineral in jewelry. ## Physical Properties Indicolite, as a variety of tourmaline, has a hardness ranging from 7-7.5 on the Mohs scale, making it relatively scratch-resistant. It possesses a vitreous luster. It is transparent to translucent, allowing for deep light penetration and the enhancement of its color. This mineral exhibits distinct pleochroism, meaning its color changes depending on the viewing angle. The fracture of indicolite is conchoidal to uneven. ## Colors and Varieties The name "indicolite" refers exclusively to blue varieties of tourmaline. Color is the key distinguishing feature of this variety. Blue shades can be very diverse, from pale, almost colorless blue, to deep indigo. Sometimes, color zoning is observed within a single crystal, where different shades of blue or even other tourmaline colors (e.g., green) occur together. ## History and Name The name "indicolite" comes from the color indigo, referring to the intense blue hue that this mineral often takes. Tourmalines, including indicolite, have been known since antiquity, but their precise classification and understanding of their diversity occurred much later. In the 18th century, Dutch merchants brought tourmalines from Sri Lanka to Europe, where they gained popularity. Indicolite, as a specific variety, was distinguished due to its characteristic color. ## Uses The primary use of indicolite is in jewelry. Its beautiful blue color and high hardness make it a prized gemstone. It is used to make rings, necklaces, earrings, and other ornaments. Larger, clean specimens are particularly sought after by collectors. Due to its piezoelectric and pyroelectric properties, tourmalines, including indicolite, also find applications in the electronics industry, though to a lesser extent than other varieties.
Diagnostic features
## Identification Indicolite can be identified by its characteristic blue color, which can range from light blue to dark indigo. Crystals often have an elongated, prismatic habit with distinct striations. Pleochroism, i.e., the change in color depending on the viewing angle, is also an important diagnostic feature. A hardness of 7-7.5 on the Mohs scale helps distinguish it from similar minerals. ## Distinguishing from Similar Minerals Indicolite can be confused with other blue minerals, such as sapphire, aquamarine, topaz, or kyanite. It is distinguished from sapphire by its lower hardness and often more complex crystal habit. From aquamarine and topaz, it differs by its pleochroism and usually more intense blue hues. Kyanite has lower hardness and perfect cleavage in one direction, which indicolite does not exhibit. The specific pleochroism of tourmalines is a key distinguishing feature. ## Crystal Forms Indicolite most commonly occurs as elongated, prismatic crystals with a triangular or hexagonal cross-section, often with rounded edges. The crystal faces are often distinctly striated parallel to the principal axis. It can also form radial, massive, or granular aggregates. Crystals are often pyramidally terminated or have complex terminations.
Geological environment
## Genesis Indicolite, like other tourmalines, forms in hydrothermal processes, mainly in granitic pegmatites and metamorphic rocks. It also occurs in quartz veins and in alluvial secondary deposits, where it is resistant to weathering. It forms over a wide range of temperatures and pressures, contributing to its diverse occurrences. ## Mineral Associations Indicolite often co-occurs with quartz, feldspar, muscovite, lepidolite, albite, and also with other varieties of tourmaline, such as elbaite or schorl. In pegmatite deposits, it can be found in association with beryl (including aquamarine), topaz, and garnets. ## Localities Significant deposits of indicolite are found in Brazil (Minas Gerais), Madagascar, Afghanistan, Pakistan, the United States (California, Maine), Russia (Urals), and Africa (Nigeria, Namibia). Brazil is particularly known for high-quality indicolites with intense colors.
Rarity
Uncommon
Collector aspects
## Quality Criteria The most prized indicolite specimens are characterized by intense, uniform color, high transparency, and the absence of visible inclusions. Clean, well-formed crystals with a distinct habit are highly sought after. The size of the stone is also important, with larger, good-quality specimens commanding higher prices. Specimens with distinct pleochroism are also valued. ## Popular Localities The most prized indicolite specimens come from Brazil, especially from the state of Minas Gerais, where rich pegmatite deposits are found. Other important sources include Afghanistan and Pakistan, known for beautiful, clean crystals, as well as Madagascar, offering a wide range of blue hues. Historically significant deposits were also found in the United States.
Care and storage
## Cleaning Indicolite can be cleaned gently with warm water and mild soap. Use a soft brush or cloth to remove dirt from the surface of the stone and from crevices. After washing, rinse the stone thoroughly with clean water and dry with a soft cloth. ## What to Avoid Avoid cleaning indicolite with ultrasonic cleaners or steam cleaners, as these can damage the stone or cause fractures, especially if the stone has internal inclusions or cracks. Avoid contact with strong chemicals, acids, and bases, which can dull the surface or change the color. Prolonged exposure to direct sunlight can, in some cases, lead to color fading. The stone should also be protected from sudden temperature changes. ## Storage Indicolite should be stored separately from other, harder minerals to avoid scratches. It is best to wrap it in a soft cloth or place it in a separate pouch or box. Store in a dry place, away from direct sunlight and heat sources.