Description
Overview and Key Features
This exceptional Green Tremolite Mineral Specimen comes from the renowned Merelani Hills in the Arusha Region of northern Tanzania — one of the most famous mineral localities in the world, celebrated for its production of gem-quality Tanzanite, Diopside, and other rare silicate minerals. This particular specimen displays the distinctive vibrant green hues of Tremolite, a member of the amphibole group of silicate minerals, known for its fibrous to bladed crystal structure and silky lustre.
All of our Fossils are 100% Genuine Specimens and come with a Certificate of Authenticity. The specimen shown in the photo is the exact one you will receive, complete with a 1cm scale cube for accurate size reference. Each Tremolite crystal has been carefully chosen for its sharp crystal form, natural colour zoning, and well-preserved fibrous habit, making it both scientifically important and visually striking.
Geological Classification and Composition
Tremolite is a calcium magnesium silicate belonging to the amphibole group of inosilicate minerals. Its chemical formula is Ca₂Mg₅Si₈O₂₂(OH)₂, and it represents the magnesium-rich end-member of the Tremolite–Actinolite–Ferro-actinolite solid solution series. The presence of iron determines its colouration: pure magnesium-rich Tremolite is white or colourless, whereas trace iron gives rise to the beautiful green shades seen in this Tanzanian specimen.
Scientific Properties:
-
Chemical Formula: Ca₂Mg₅Si₈O₂₂(OH)₂
-
Crystal System: Monoclinic
-
Mineral Group: Amphibole
-
Hardness: 5–6 (Mohs scale)
-
Specific Gravity: 2.9–3.1
-
Lustre: Silky to vitreous
-
Transparency: Translucent to semi-transparent
-
Cleavage: Perfect on {110}
-
Fracture: Splintery
-
Streak: White
-
Habit: Fibrous, acicular, or bladed crystal aggregates
The amphibole structure is composed of double chains of silicon–oxygen tetrahedra bonded to metal cations. Tremolite’s unique fibrous crystal habit reflects this chain-like silicate arrangement, giving rise to elongated needle- or blade-shaped crystals that can intergrow in parallel bundles. The fibrous form seen here is typical of metamorphic environments rich in magnesium and calcium.
Geological Formation and Origin
This green Tremolite crystal originates from the Merelani Hills, located near Mount Kilimanjaro in northern Tanzania. The area lies within the Lelatema Fold Belt, a Proterozoic metamorphic terrane formed approximately 600 million years ago during the Pan-African orogeny. Tremolite forms here through regional metamorphism of dolomitic limestones and ultramafic rocks, where magnesium-rich fluids and elevated temperatures cause recrystallisation into amphibole minerals.
Within the Merelani geological sequence, Tremolite occurs in association with:
-
Tanzanite (blue Zoisite)
-
Graphite
-
Diopside
-
Prehnite
-
Calcite and Quartz
The presence of Tremolite in this region is a clear indicator of high-grade metamorphism under amphibolite facies conditions, where pressures and temperatures reach approximately 500–700°C. The green colouration of this specimen reflects trace iron substitution for magnesium within the crystal lattice, producing its distinctive hue.
Merelani Hills’ unique combination of graphitic schist, dolomite marble, and metamorphosed ultramafic rocks creates the perfect environment for the formation of well-developed Tremolite crystals. The mineral typically crystallises in cavities or foliations, sometimes forming elongated radiating clusters that reflect metamorphic flow directions within the host rock.
Morphology and Physical Characteristics
This specimen displays the classic fibrous to bladed crystal habit characteristic of Tremolite, with elongated crystals arranged in parallel alignment and a silky sheen across their surfaces. The natural green colour zoning is due to subtle variations in iron content throughout crystal growth.
-
Crystal Habit: Bladed and fibrous intergrowths
-
Colour: Vibrant green with hints of pale green or white
-
Texture: Smooth, with slight fibrous sheen under magnification
-
Transparency: Translucent to opaque
-
Associations: Found with Graphite, Calcite, and Diopside in metamorphic host rock
Under strong light, this specimen exhibits a subtle internal shimmer, with light reflecting off fine fibrous cleavage surfaces. When viewed under magnification, the acicular crystals show parallel growth, a defining feature of the amphibole group.
Scientific and Mineralogical Significance
Tremolite is of considerable scientific and educational value due to its role in understanding metamorphic mineral assemblages and rock evolution. It serves as an index mineral for determining metamorphic grade in calcium- and magnesium-rich environments. The mineral’s composition can indicate metamorphic temperature and pressure conditions, as well as the chemistry of the original protolith.
Tremolite is also of interest in mineralogical research because of its structural position within the amphibole family. It represents the magnesium end-member, contrasting with the iron-rich Actinolite, providing a valuable reference for understanding amphibole solid solution systems.
In industrial mineralogy, fine fibrous forms of Tremolite have been studied for their asbestiform properties, though this particular specimen is non-asbestiform and collected solely for its aesthetic and geological value. Its fibrous texture is naturally compact, making it safe for display and handling.
Aesthetic and Collectible Value
Collectors prize Tremolite specimens from the Merelani Hills for their striking green hues, well-defined fibrous crystals, and geological association with the famous Tanzanite mines. The mineral’s vivid natural colour, combined with its metamorphic origin, makes it a beautiful addition to any display of African minerals.
When displayed under direct light, the specimen reveals subtle variations in tone and internal sheen that bring its fibrous nature to life. It can be showcased alongside other metamorphic minerals such as Diopside, Zoisite, or Garnet to highlight regional geological relationships.
To preserve its natural lustre, store in a dry environment away from direct sunlight or humidity. Clean gently with a soft, dry cloth only.
This Green Tremolite from Merelani Hills, Tanzania represents a remarkable intersection of natural artistry and scientific significance — a crystalline record of metamorphic evolution preserved in vibrant green amphibole form. A fine addition to any geological collection, educational setting, or private mineral display.
Reviews
There are no reviews yet.