Cylindrite

Chemical formula: FePb₃Sn₄Sb₂S₁₄

Cylindrite is a rare sulfosalt mineral, distinguished by its unique crystal form, which appears as lamellae rolled into tubes or cylinders.

## Characteristics Cylindrite is a complex sulfosalt of lead, tin, iron, and antimony. Its most characteristic and unique feature is the form in which it crystallizes. Instead of typical polyhedral crystals, it forms aggregates composed of concentrically rolled lamellae, which look like small tubes, cylinders, or scrolls. Individual "tubes" can be separate or grown together into larger, irregular masses. The surface of these forms is often striated or grooved along their length. The mineral has a metallic luster and a dark, grayish-black color. ## Physical Properties Cylindrite is a relatively soft mineral, with a hardness of approximately 2.5 on the Mohs scale, meaning it can be scratched with a fingernail. It has a high specific gravity, around 5.43 g/cm³, which is noticeable even in small specimens. It exhibits a strong, metallic luster. It is completely opaque. ## Colors and Varieties This mineral is uniform in color, occurring in shades from steel-gray to black. It does not form color varieties or possess distinct trade names. Its value and recognition stem solely from its unique morphology. ## History and Name Cylindrite was first described in 1893. Its name, given by the German mineralogist August Frenzel, comes from the Greek word *kylindros* (κύλινδρος), meaning "cylinder" or "roller," which is a direct reference to its unusual crystalline form. The type locality, from which the first studied specimens originated, is the Santa Cruz mine in Poopó, Bolivia. ## Uses Cylindrite has no industrial applications. It is a mineral of purely scientific interest and is highly valued and sought after by collectors due to its exceptional and rare form.

Properties

Mohs hardness: 2.5
Luster: Metallic
Streak: Black
Density: 5.43
Cleavage: On {100}
Fracture: Uneven
Transparency: Opaque
Crystal system: Triclinic

Diagnostic features

## Identification The most important diagnostic feature of cylindrite is its unique form as cylindrical or tubular aggregates. No other mineral regularly forms such structures. Additional clues include its metallic luster, high density, low hardness (approximately 2.5 on the Mohs scale), and a black streak. ## Distinguishing from Similar Minerals Cylindrite is sometimes confused with other sulfosalts from the same group, such as franckeite or incaite, which can also form similar, though usually less perfect, rolled forms. Franckeite often has flatter, less cylindrical lamellae. Accurate differentiation within this group of minerals often requires chemical analysis. From stibnite, which also forms elongated crystals, it is distinguished by the lack of distinct longitudinal cleavage and its cylindrical cross-section. ## Crystal Forms Cylindrite does not form classic, euhedral crystals. It occurs as cylindrical or tubular aggregates, which are in fact lamellae rolled into scrolls. The diameter of these cylinders rarely exceeds a few millimeters, and their length can reach several centimeters. They often occur as tangled or radiating aggregates.

Geological environment

## Genesis Cylindrite is a hydrothermal mineral, forming in ore veins at relatively low to medium temperatures. Its formation is associated with crystallization from complex solutions rich in lead, tin, antimony, iron, and sulfur. ## Mineral Associations It most commonly co-occurs with other sulfides and sulfosalts, such as stannite, franckeite, incaite, jamesonite, cinnabar, pyrite, marcasite, sphalerite, and quartz. It often forms intergrowths with other minerals from the cylindrite group. ## Localities The most important and globally renowned deposits, from which the best collector specimens originate, are found in Bolivia, particularly in the Oruro region (Santa Cruz, Trinacria mines) and Potosí. This is the classic locality for this mineral. Occurrences have also been reported in small quantities in Russia (Siberia) and the USA.

Rarity

Rare

For collectors

## Quality Criteria The most highly valued specimens by collectors are those with well-formed, distinct, and undamaged cylinders. An ideal specimen should display sharp, uncrushed "tubes" with good metallic luster, preferably contrasting with the surrounding host rock (matrix). Large, rich aggregates of many cylinders or specimens with exceptionally long and slender forms command the highest prices. The overall aesthetic composition is also important. ## Popular Localities By far the most desirable specimens come from historical localities in Bolivia, especially from mines around Poopó in the Oruro department. Specimens from these locations are considered the global standard for cylindrite.

Care and storage

## Cleaning Cylindrite specimens are very delicate and soft. To remove dust, use only a soft brush or a careful stream of compressed air from a safe distance. Avoid wet cleaning, and especially the use of ultrasonics, which can destroy delicate structures. ## What to Avoid The mineral is sensitive to chemicals, including acids and bases. It should be protected from scratches, impacts, and falls, as it is brittle and soft. Prolonged exposure to moisture can lead to slow oxidation and dulling of the surface. ## Storage It is best to store specimens in separate, padded collector's boxes to prevent abrasions and mechanical damage. Do not place it in the same container with harder minerals. Display should be in a closed cabinet, protecting it from dust and damage.