Emerald Education
Emerald is the vibrant green to bluish-green variety of beryl, a mineral species that also includes aquamarine and other colored beryl.
Emerald falls within the chemical class of silicates, specifically the subclass of cyclosilicates. Its name is linked to its distinctive green hue, which results from the presence of chromium, iron, and vanadium impurities substituting aluminum in the crystalline structure. The intensity of the color depends on the concentration of these elements within the beryl’s chemical composition (Souza et al., 1987).
Emeralds rank 7.5 to 8 on the Mohs hardness scale (1–10), a key property for gemstones used in jewelry. Another remarkable feature is pleochroism, an optical phenomenon where a mineral shows different colors when viewed from varying angles. In authentic emeralds, pleochroism ranges from yellowish-green to bluish-green. Their relative density typically ranges from 2.670 to 2.780 (Sinkankas, 1981). Measurements of crystals from the Belmont Mine have recorded an average density of 2.710 (±0.020) (Sauer, 1982).
It is rare to find an emerald without inclusions, which occur in various forms. The descriptive analysis and classification of inclusions are crucial in determining whether a gemstone is of natural or synthetic origin.
Emeralds from the Itabira/Nova Era region are particularly known for a high concentration of fluid inclusions, with fluid types predominating over crystalline ones (Souza, 1988; Machado, 1994). This characteristic is also strongly present in emeralds from the Belmont Mine. Similar to other deposits in the Itabira/Nova Era area (Souza, 1988), Belmont emeralds display internal cavities or growth tubes that are typically oriented in parallel. This creates the distinctive “rain effect” (Schwarz, 1987). These cavities may contain liquid, gas, and solid phases, ranging from biphasic to polyphasic. The effect is easily observed when clusters of these inclusions align with the crystal’s growth direction (Photomicrographs 01).
Photomicrograph 01: Detail of growth tubes oriented in a preferential direction called “Rain Effect” in a Belmont emerald, unique characteristic of the minerals from this region. (100x and 200x magnification).
Where Emeralds are Sourced
Although authentic emeralds have been found in many parts of the world. The rarity of this Beryl variety makes it, together with diamond and alexandrite, the most coveted gemstones in the world, reaching high values.
In addition to Brazil and Colombia in South America, authentic emeralds have been found in Russia, Afghanistan, Pakistan, India, Austria, Australia, Zambia, Zimbabwe, Tanzania, Madagascar, Nigeria, South Africa, USA, Norway, Spain and Egypt (Figure 01). In the Industry, most emerald crystals come from Colombia, Brazil and Zambia.
In Brazil, authentic emeralds are mined in the states of Goiás (Campos Verdes), Bahia (Campos Formoso/Pindobaçu and Anagé) and Minas Gerais (Itabira/Nova Era, in São Domingos do Prata and Esmeraldas de Ferros). Other occurrences can be mentioned, such as Tauá (in Ceará); Monte Santo (Tocantins); Tenente Ananias (Rio Grande do Norte).
The main companies producing this mineral good are: Belmont Mineração and Canaã Indústria e Comércio located in Itabira (MG); Itaobi in Campos Verdes (GO), Brazil. And Gemfields in Zambia.
Figure 01: Map indicating emerald occurrences in the world.
Emerald Geological formation
There are mainly two types of genetic classification for authentic emeralds: the Colombian type, with the typical example of Colombian mines and the classical or shale type, with beryllium source through pegmatite contribution or not, covers most of the known deposits worldwide. Examples of occurrences of this type are in Brazil.
Shale deposit authentic emeralds are normally disseminated in dark shale and results from the chemical interaction of residual solutions of granitic rocks, enriched in beryllium, with basic/ultrabasic rocks that supply the iron, chromium and vanadium chromophores.
Historically, emerald deposits have been classified into three broad types. The first and most abundant deposit type, in terms of production, is the desilicated pegmatite related type that formed via the interaction of metasomatic fluids with beryllium-rich pegmatites, or similar granitic bodies, that intruded into chromium- or vanadium-rich rocks, such as ultramafic and volcanic rocks, or shales derived from those rocks.
A second deposit type, accounting for most of the emerald of gem quality, is the sedimentary type, which generally involves the interaction, along faults and fractures, of upper-level crustal brines rich in Be from evaporite interaction with shales and other Cr- and/or V-bearing sedimentary rocks.
Emerald Mining
Artisanal mining is widely performed for the extraction of gemstones. Emeralds are no different. Usually, workers use rudimentary equipment to open galleries with no technical planning for the work and for the disposal of the materials called sterile waste. The mineral recovery and the operating conditions are often inefficient and unsafe. People involved in the mining work rarely use proper protective equipment. Consequently, affecting the quality of life of these employees over time.
Investments in mining state-of-the-art mining technology are important to improve operational efficiency, safety, and production workflow. Mining engineers must develop a mining plan according to the geological model of the mineral assets of economic interest. Their assessment is important to determine the type of mine to be implemented and the methods to be used to operate the mine.
Photo 01: Gallery excavated through artisanal work.
The chosen equipment should be compatible with the characteristics of the mine to be developed as well as the geometry and dimensions planned by engineering. Equipment manufacturers are often developing new technologies in order to optimize the mining activity.
Both open pit and underground mines are developed through the use of standards established by local mineral legislation. Aiming at a pleasant, safe and efficient work environmental.