Проектная деятельность на тему "Изумруды"

Presentation on the subject" of Emeralds"

The origin of emeralds

Emeralds are formed by the interaction of acidic magma with host ultrabasic igneous rocks, so their deposits are represented by zones of greisenization. Occasionally small emeralds are formed in exocontacts of pegmatites.

In most deposits of the world, emerald is confined to phlogopite mica formed as a result of greisenization — the effect of high-temperature aqueous solutions on ultrabasic rocks. As a result of this process, the original rocks due to feldspar granites are transformed into multi—complex rocks with quartz, light micas and often valuable ore minerals in the form of inclusions. The presence of greysens is a leading search sign for deposits of rare metals and precious stones, including emerald.

history

• Emeralds were highly valued by ancient cultures, and the inhabitants of Babylon traded them as early as 4000 BC. The famous emerald mines of Cleopatra were located in the vicinity of Aswan (Egypt). For centuries it was believed that these mines were just a legend, but in 1818 they were reopened. At that time, few emeralds were found in them, but tools were found in the mine, which, as it was later determined, dated back to 1300 BC. Emeralds were also valued by the rulers of India. It is believed that Sultan Shah Jahan, the builder of the Taj Mahal, wore emeralds engraved with sacred texts as a talisman.

Colour

The color of the stone is divided into three components: tone, saturation and lightness. Emeralds come in various shades — from yellow-green to blue-green, but the main tone is necessarily green, up to the darkest green tone.

The color distribution of the emerald is uneven: usually the free end of the crystal is colored brighter than its base, there are also zonal crystals with a longitudinal change in color intensity (often with a brighter core) and with a transverse alternation of light and dark green zones. In brightly colored stones, dichroism is noticeable even to the eye — a change in color from yellowish to bluish-green when the crystal is rotated.

Hardness and fracturing

Natural emeralds are rarely defect-free, they usually have cracks and splits, often they are dissected by a complex network of thin veins and cracks. Increased brittleness is a characteristic feature of the stone: its hardness is 7.5—8 on the Mohs scale (for diamond — 10), in combination with thin cracks of transverse separation, this makes it very sensitive to compression and heating.

Unlike a diamond, where the quality is standardly assessed at 10x magnification, an emerald is assessed by eye: a stone that does not have visible cracks (provided normal visual acuity) is considered flawless.

Deposit

• Good emeralds are rare, most of them are found in the Colombian Tunkha deposits (the deposit was discovered in 1555) and Muso (known since 1537), in New Granada, Zambia, Brazil and Egypt. Emeralds of lower quality are found in Habachtal, in Salzburg (Austria), in the Mourne Mountains (Ireland), on Lake Mezen (Norway) and in some other localities

• Emeralds are also mined in Russia, USA, Canada, Australia, Spain, France, Switzerland, Italy, Germany, Bulgaria, Kazakhstan, Pakistan, Afghanistan, India, China, Cambodia, Egypt, Ethiopia, South Africa, Somalia, Nigeria, Namibia, Tanzania, Zimbabwe, Mozambique and Madagascar.

Emeralds of Colombia

• Nowadays, from 50 to 95% of the production of all emeralds falls on Colombia (the specific percentage varies greatly from year to year in different directions. In the period from 2000 to 2010, the volume of emerald production in Colombia increased by 78%. In addition to the usual emeralds, trapiche is also mined in Colombia-an emerald that distinguishes the formation of crystals in the form of a wheel with spokes.

Emeralds of Afghanistan

• Afghan emeralds or Panjshir emeralds are mined in the upper reaches of the Panjshir gorge, in the Pavat area, in the villages: Piryah, Mabain, Zaradhak — 10-13 kilometers south-east and east of the settlement of Pishgor, in each of which 20 to 40 mines were concentrated, as well as significant deposits of emeralds are located in the Darkhinj gorge.
• During the Afghan War (1979-1989), the development of emeralds in the Panjshir Gorge was under the control of a major field commander Ahmad Shah Massoud. After extraction, the emerald was sent to Pakistan for processing, and from there it was distributed to international markets.
• The amount of funds raised for emeralds during this period, on average, amounted to $ 10 million per year. Mining operations on rocky soils were carried out by Japanese drilling rigs with the involvement of Western European engineers.
• According to jeweler Oded Burstein, Afghan emeralds are a worthy alternative to emeralds from Colombia and Zambia, they are even better, because the crystal of the Afghan emerald is cleaner and denser, and emits more bright luster, has a unique shade[18].