Clinozoisite

Chemical formula: Ca<sub>2</sub>Al<sub>3</sub>(Si<sub>2</sub>O<sub>7</sub>)(SiO<sub>4</sub>)O(OH)

Calcium aluminum silicate from the epidote group, forming prismatic crystals with colors ranging from greenish and gray to pink and brown.

## Characteristics Clinozoisite is a mineral belonging to the epidote group, forming an isomorphic series with epidote and piemontite. It is a polymorph of orthorhombic zoisite. It forms elongated, prismatic crystals, often terminated by steep faces. Crystals can be longitudinally striated. It also occurs in granular, radial, fibrous aggregates or massive forms. ## Physical Properties Clinozoisite has a hardness of 6-7 on the Mohs scale. It exhibits a vitreous luster, and a resinous luster on fracture surfaces. It is a relatively dense mineral, with a density of approximately 3.21-3.38 g/cm³. It is brittle and shows perfect cleavage in one direction. ## Colors and Varieties The most common colors of clinozoisite are shades of green (grayish-green, pistachio), brown, gray, and yellow. Less commonly, it can be colorless, pink, or purplish. Some pink, manganese-rich varieties are sometimes mistaken for thulite (a variety of zoisite), but they differ in their crystal structure. ## History and Name The mineral's name, given in 1896 by Ernst Weinschenk, refers to its monoclinic symmetry and chemical similarity to zoisite. It was separated as a distinct mineral from the previously known epidote based on more precise chemical and crystallographic analyses. ## Uses Transparent and attractively colored clinozoisite crystals are occasionally faceted and used as gemstones for collectors. However, due to its brittleness and perfect cleavage, it is not a popular jewelry material. The primary significance of clinozoisite is scientific and for collecting.

Properties

Mohs hardness
6-7
Luster
Vitreous, resinous
Streak
White
Density
3.21-3.38
Cleavage
Perfect on {001}
Fracture
Uneven to conchoidal
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Clinozoisite is most easily identified by its characteristic, elongated, and often striated prismatic crystals. Important features include its vitreous luster, hardness (scratches glass), and perfect cleavage in one direction. It occurs in specific metamorphic environments. ## Distinguishing from Similar Minerals Clinozoisite is difficult to distinguish from epidote without specialized tests. Typically, epidote has a more intense, pistachio-green color, while clinozoisite is lighter, more grayish, or brownish. Definitive differentiation requires optical or X-ray analysis. It can also be confused with vesuvianite, diopside, or tourmaline, from which it differs in crystal form, hardness, and cleavage. ## Crystal Forms Crystals are typically columnar or prismatic, often elongated along one axis and longitudinally striated. It also occurs in granular, fibrous, radial aggregates, or as compact, massive aggregates.

Geological environment

## Genesis Clinozoisite is a typical mineral of metamorphic rocks. It forms under conditions of low- to medium-grade regional metamorphism, in the greenschist and amphibolite facies. It is also a product of contact metasomatism in carbonate rocks (skarns) and hydrothermal alteration of plagioclase (saussuritization). ## Mineral Associations It often co-occurs with other minerals from the epidote group (epidote, zoisite), as well as with actinolite, chlorite, albite, quartz, calcite, vesuvianite, diopside, and garnets (mainly grossular). ## Localities Significant deposits and well-formed clinozoisite crystals come from many places around the world. The most important include the Ala Valley and Viù Valley in Piedmont (Italy), Knappenwand in the Untersulzbach Valley (Austria), the Zermatt area (Switzerland), California and Colorado (USA), as well as Mexico, Pakistan, Kenya, and Madagascar.

Rarity

Not very common

For collectors

## Quality Criteria The most prized by collectors are well-formed, sharply terminated, transparent crystals with vivid colors - especially pink, yellow, and light green. Large, undamaged crystals and aesthetic growths on matrix rock are also highly valued, particularly when associated with other minerals such as diopside, garnets, or quartz. ## Popular Localities Gem-quality specimens and the best collector crystals mainly come from Pakistan (Shigar Valley), Mexico (Baja California), Kenya, and from Alpine fissures in Austria and Switzerland. Classic, historical localities are found in Italy (Piedmont).

Care and storage

## Cleaning Clinozoisite specimens can be safely cleaned with lukewarm water and mild soap, using a soft brush. Ultrasonic cleaners should be avoided, as they can cause fractures along cleavage planes. ## What to Avoid The mineral is sensitive to strong acids, especially hydrofluoric acid. Avoid sudden temperature changes, which can lead to internal cracks. It should not be exposed to prolonged direct sunlight, although its color is generally stable. ## Storage Due to its relatively good hardness, clinozoisite is not particularly prone to scratching, but its brittleness and cleavage require caution. It is recommended to store specimens in separate boxes or on a soft surface to avoid impacts and pressure that could cause fragments to chip off.

External references

Sources

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