Located approximately 135 km north of Quetta, in the Balochistan province of Pakistan, the Killa Saifullah region is world-renowned for the exceptional quality of its brucite, a rare and remarkable mineral species. This district is part of the vast ophiolitic complex of the Zhob Valley, which marks the tectonic boundary between the Indian and Eurasian plates. This particular geodynamic context favors the formation of numerous minerals of scientific and economic interest, including brucite, which occupies a central place due to its striking aesthetic.

Photo : Brucite from Killa Saifullah, Pakistan © Rémi Bornet

The Muslim Bagh ophiolitic complex, one of the best exposed in Pakistan, represents a fragment of oceanic lithosphere obducted during the collision between the Indian and Eurasian plates. It is subdivided into two main massifs : Jang Tor Ghar to the west and Saplai Tor Ghar to the east. This complex comprises a complete ophiolitic sequence, structured according to classical principles:

• A mantle section composed mainly of peridotites, such as harzburgite, lherzolite, and dunite, which exhibit a high rate of serpentinization.
  
  
• A dunite-rich transition zone, often intensely altered, hosting exploitable concentrations of chromite.
  
  
• An oceanic crust composed of gabbros, dykes, and pillow basalts.

The complex is crowned by a metamorphic sole and rests on Mesozoic sedimentary series. This complex tectonic and metamorphic framework allows the establishment of multiple hydrothermal episodes responsible for the formation of secondary minerals such as brucite.

Brucite (Mg(OH)₂) is formed by metasomatic transformation of ultramafic rocks, mainly dunites, during the serpentinization process. This phenomenon is triggered by the circulation of hydrothermal waters rich in carbon dioxide and dissolved silica, which react with magnesium olivines (forsterite) according to the following reaction :

Forsterite (Mg₂SiO₄) + H₂O → Serpentine + Brucite

In the Muslim Bagh peridotites, brucite typically appears at an advanced stage of serpentinization, in association with mineral phases such as magnesite or chrysotile and antigorite (serpentine). Microscopic observations reveal its presence in fibrous or botryoidal aggregates, filling microcracks or bordering serpentinized veins. Locally, it can constitute up to 20% of the volume of the rock, notably in the highly altered dunites of the transition zone.

Killa Saifullah brucite is a magnesium hydroxide with the formula Mg(OH)₂. It crystallizes in the trigonal system, often with lamellar crystals, although Pakistani samples most frequently occur in massive or botryoidal form. Its structure consists of sheets of Mg²⁺ cations coordinated with hydroxyl groups, which gives brucite a perfect basal cleavage along the {0001} plane. This configuration makes it extremely sensitive to mechanical pressure, humidity, and heat.

Its very low hardness (2.5 on the Mohs scale) limits any practical use in jewelry. Only a few faceted stones for museum or collector purposes exist, and their handling requires great caution. Its refractive index ranges from 1.58 to 1.60, and its relatively low density of around 2.39 g/cm³ is typical of hydroxyl minerals.

Killa Saifullah specimens are recognized for their distinctive colors ranging from bright lemon yellow to translucent light green, sometimes nearly colorless. This color palette is likely influenced by traces of minor elements (Fe²⁺, Ni, Mn). Their pearly to silky luster and translucency make them particularly attractive to collectors.

Brucite deposits located in the southern Nisai region, near the village of Ekhai (Khuzdar district, Balochistan, Pakistan), are mined artisanally, without the use of heavy mechanization. Mining is carried out open-pit, in mineralized lenses and veins hosted in dunites, often at very shallow depths. The extracted masses are sorted manually, based on visual criteria such as color, texture, and shape, to distinguish samples intended for the collector market from those potentially usable as raw materials.

Economically, brucite from Balochistan is of growing interest. It is used industrially as a natural flame retardant, particularly in plastics, rubber, and electrical cables, thanks to its thermal stability and ability to release water during decomposition. It also serves as a mineral filler in polymers and composite materials, as well as a base neutralizer in various chemical and environmental processes, including the treatment of wastewater and acidic soils. These uses are well developed in countries such as China, South Korea, and Japan, where part of Pakistani production is exported.

The market value of specimens for collectors depends heavily on the crystalline quality, color intensity, and the integrity of the extracted pieces, particularly when they exhibit aesthetic associations with carbonates (hydromagnesite) or other secondary phases.

The Muslim Bagh complex and its immediate surroundings contain a wide variety of minerals resulting from hydrothermal and metasomatic alterations typical of ophiolitic complexes :

• Chrysocolla, malachite, and azurite : formed by supergene alteration in copper-rich zones of basalts and gabbros.
  
  
• Epidote : crystallized in dolerite dykes, often associated with actinolite.
  
  
• Garnet (almandine, tsavorite): present in amphibolitic layers of the metamorphic sole, related to amphibolite facies conditions.
  
  
• Fluorite and calcite : precipitated in late Triassic carbonate fractures (Loralai Formation), likely as a result of late hydrothermal circulation.

The brucite of Killa Saifullah, and more broadly of the Muslim Bagh ophiolitic complex, constitutes a remarkable example of secondary mineralization in an altered mantle context. Its study offers a valuable window on the hydrothermal processes affecting peridotites in ophiolitic systems. While its use in jewelry remains nonexistent due to its unfavorable mechanical properties, its beauty, rarity, and the purity of certain specimens make it a sought-after reference for museums and collectors. In the future, geoscientific and heritage valorization of these sites could contribute to the international recognition of Balochistan as a mineralogical province of global interest.