Types of deposits and geographical distribution of gems

Gems are found in almost all types of rocks, although with different frequency in each other. If taken together, they probably constitute the group of minerals that best represent the variations in pressure and temperature that can give rise to the different types of known deposits in the earth’s crust. They can be formed by primary crystallization from acidic, intermediate, basic and ultrabasic magmas, by recrystallization in metamorphic rocks, by weathering and dragging of pre-existing rocks, by chemical precipitation, by organic action and by the combined action of all the previous processes.

Types of deposits of the main gems.

Excluding diamonds, which alone constitute 90% in value of all marketed gems, and pearls, which today are practically all cultivated, the gems are distributed in the different deposits as follows:

Approximately 25% of all gems have an igneous origin, mainly pegmatitic.

30% can be found in metamorphic nesting rocks, whether they are calcareous or non-calcareous.

Another 30% corresponds to deposits of aqueous origin (hydrothermal, surface circulating water, etc.)

15% to gems of organic origin (ambercoralivory, etc.).

Geographical distribution of the main gems.

From a geographical point of view, all continents have important deposits of gemological material:

In Asia there are the most important ruby deposits, especially in Mogok and Hong-Hsu ( Myanmar, former Burma ). In Southeast Asia (Thailand , Myanmar, Indochina and Sri Lanka) are, in turn, the most important deposits of sapphires , spinels and zircons , in Kashmir (India) the best sapphires have appeared, from Afghanistan stand out their exceptional lapis lazuli, large jade deposits are found in Myanmar and China , while historically, diamond and many varieties of quartz have had some of their main deposits in India . In Siberia (Russia) there are important deposits of diamond, chrysoberyl and many other gems.

The most important and varied stones found in South America are found in the Brazilian shield. The State of Minas Geraes is justly famous for its abundance and variety in gems; diamondstopazes ,emeraldsaquamarinesmorganites and other berylsspinelsgarnetskunzitestourmalinesquartz of all varieties and practically all pegmatitic gems, as well as many of the metamorphic ones appear.

Spain is a country, as a whole, poor in gems.

  • It lacks diamonds , which have been unsuccessfully investigated in the ultrabasic massifs of Ojén and Carratraca (Málaga) and in the ultrapotassium volcanic rocks of Jumilla (Murcia). Detailed gemological research has been published by various authors (García GuineaGalan).
  • Beryls are frequent, but not gem quality.
  • Some emeralds , of very little gemological value, have been found in the complex of Lalín (Pontevedra).
  • Also blue-green aquamarines , some large, in Pereña and other towns in Salamanca .
  • There seems to be no corundums or spinels of gem quality.
  • Tourmalines , abundant in the granitic massifs of the Western Peninsula, are always black (chorlo) and therefore have no gemological value.
  • Colorless and blue topazes have been found in the Valle de la Serena (Badajoz), but they are far from the value of the imperial topazes of Brazil.
  • Citrine and smoky quartz of large size and good quality have been found in Villasbuenas ( Salamanca ) and variscita in Palazuelos de las Cuevas (Zamora).
  • Garnets in various locations ( Níjar , Salamanca , La Coruña , etc.).
  • Some agates and chalcedony of a certain beauty and few other things.

In the United States of America there are important deposits of sapphiresgarnetsspodumenetourmalineturquoisetopaz, red beryl and other gems. In Mexico , fire and noble opals are famous, as well as amethysts from the state of Guerrero. The topazes of San Luis Potosí also stand out, as well as the Nephrites and Obsidians .

Africa is also an extraordinarily rich continent in gems. There are diamonds in great quantity and with gem quality in South Africa , Ghana , Angola , Bostwana , Namibia , Sierra Leone , Democratic Republic of the Congo , Tanzania and other countries of Central and Southern Africa. Chrysoberylemeraldgarnetssapphire and ruby, tiger’s eye, tourmaline and zircon in Zimbabwe , South Africa , Kenya and Tanzania . Olivine and turquoise in Egypt . Madagascar is very rich in quartzfeldspargarnetscapolitesphenespinelspodumeneberyl and many other gems.

Finally, Oceania is also a very rich continent, although the discoveries are more recent. Australia is one of the world’s leading producers of diamonds (highlighting, among others, the rare and valuable “fantasy” diamonds), and has large deposits of sapphireopalspinel and turquoise .

Colombia To Host World Emerald Symposium in October


Colombia is to hold the first gathering of the world emerald industry, and is inviting all emerald producing countries to take part in the event in Bogota from October 13 to 15. The conference will be followed by a visit to the famous Muzo emerald mine.

The countries invited to attend the conference include Zambia, Brazil, Russia, Afghanistan, Pakistan and Madagascar. In addition, all relevant players are being invited, including governments, the private sector, civil society and all sectors of the emerald mining and manufacturing industry.

The conference will provide a comprehensive analysis of all elements of the emerald industry, including geology, mining, resource management, laws and regulations, manufacturing, treatments, marketing, nomenclature, labs and certification, education, origin and traceability, harmonization of the sector at the global level, relations with consumers, jewelry, branding and overall supply chain integration from mine to market.

The issues will be addressed by high-level experts from governments and the gemstone industry from a range of relevant countries, and there will also be discussions and working groups looking at the promotion of emeralds and addressing industry challenges.

The official program of events, debates and discussions is due to be released shortly. The overall aim of the conference is to boost the image of emeralds as a valuable stone and to deal with a wide range of issues, including safety in mine production and transport and emeralds as a leading global precious gemstone and store of value and to enable the global emerald industry to have a common language and unified approach.

An organized visit of delegates to the emerald mine in Muzo and surrounding area will take place on October 16.

The official organizers of the conference are: the Ministry of Mines of Colombia; Agencias Nacional e Mineria ANM (National Mining Agency); Fedesmeraldas (the Colombian Emerald Federation); ACODES (the Emerald Exporters Association); APRECOL (the Colombian Emerald Miners Association); and ASOCOESMERAL (the Colombia Emerald Dealers Association).

Source : gemstone.org/

A look at the emerald trade from rough crystals to gemstones and how the offices work in Colombia



An exceptionally large, finest rough emerald crystal from Muzo. This was offered at $45,000 wholesale price in Bogota’ in 2004. It cut two stone (match pair) of squares 7 cts. each.


Viewing an emerald rough with loupe on the famous Catorce or emerald market in Bogota.

Emerald Buying

Many of the brokers are women. My best stone during that trip, an exceptionally clean Muzo stone, heart shape of 5.65 ct. was purchased from a beautiful, female broker…nothing new about this selling tactic…except that it works well for the seller.

Emerald check

Checking emeralds. To know emeralds quality and price takes a lot, lot of experience. Checking emeralds under special loupe. A careful, close-up examination is very important. There are many synthetics offered to foreign buyers.

Sorting emerald clean parcel

A fine parcel of emerald crystals is examined. Technician checking more emeralds at a typical office. A master cutter, initializing the cutting process of an exceptional emerald crystal. This process is thought through very carefully before the cutting begins.

Emerald cutter

The master cutter’s wheel and examining the emerald crystal and try to decide how to get rid of the included section (whitish portion in the emerald crystal). Probably that occurred when the crystal was broken away from the rock host (matrix).

Muzo pair fine gota de aceite 8.50 cttw

Here is the final result: Finest color, top clarity and awesome cutting for this finest match pair, 8.5 cttw. from the Muzo crystal seen previously. In Colombia, top emeralds are called “gota de aceite”, that means “oil drop”. Were offered for sale in November 2004 in Bogota for several thousands of USD per carat.