< Ores and Minerals
Gold
Au

The chemical symbol for gold is Au and stands for the Latin word for gold, Aurum. The word gold derivates from the Old English or Old German "gulth" meaning bright or "ghol" meaning yellow as the Sanskrit word for it "jval" meaning to shine.

Gold was always valuable for the people over the centuries, mainly due to the following chemical and physical properties:
• It is a very stable chemical element and does not react with most acids, alkalis and most chemical elements.
• Does not oxidize in the oxygen environment.
• Is not rejected by living organisms because it does not cause chemical reactions in the organic substances - that makes it extremely used in medicine.
• Does not cause allergies.
• Gold is very malleable and can easily be turned into a wire, thin foil or another shape. This makes it a favourite material in jewellery.
• Provides good thermal and electrical conductivity - in combination with the fact that it can be easily shaped in thin stripes and is resistant to oxidation, which makes it widely used for microprocessors.
• Gold plating as a corrosion resistant barrier for conduits, church domes or spacecrafts.
• The gold film reflects infrared rays and is used for reflectors in space satellites.
• A little known fact is that gold is one of the heavy metals - heavier than lead.

Still, gold would not be as valuable if it wasn't so rare.

Gold is a native element mineral. It crystallizes in the cubic crystal system. Crystals are rare. Native gold is almost always contaminated, often contains 10-15% silver. Its color is yellow in different shades. When mixed with silver, it is white; mixed with copper, a reddish colour. Gold has a strong metallic lustre. Compared to all other metals, gold has high plasticity and ductility. For example, 1 gram of gold can forge a leaf with size of 1 m2. It is a very soft metal with Mohs hardness between 2.5 to 3. Therefore, when pressed with a steel needle it can be deflected or cut with a knife. The mass of absolutely pure gold is 19.320 (ie 1 cubic centimetre weighs 19.32 grams). When there are impurities it varies from 15.6 to 19.2 g/ccm, depending on their amount. For comparison, the relative mass of silver is 10.5; copper 8.93; platinum 21.46. This indicates that differences in the weight of gold can be due to the amount and type of impurities. The melting point of gold is met at 1 064,18 °C.

The greatest difficulty in gold mining (gold panning in our case) is to distinguish the gold dust from other minerals. Most often it occurs in the form of rounded grains, nuggets, flakes, wafers, etc. dendrites. The surface of the nuggets is uneven, with different shapes and sizes grooves. Sometimes it is covered with iron hydroxides, which conceal it. Most often gold can be distinguished by its gold-yellowish colour, strong metallic lustre and great malleability. It is enough to press with a needle on a gold flake to leave a mark on it. When gold comes in the form of small nuggets and flakes, often gets confused with pyrite and chalcopyrite, which are therefore called fool's gold. Pyrite is easily recognized by its greater hardness and clear cubes, and the Chalcopyrite by its fragility. Partially weathered flakes of biotite (black mica) with golden colour sometimes can also be confused with gold dust, especially in wet condition. The modified mica differs from gold in its relatively small weight, which prevents it from accumulating in heavy fraction with gold. On the other hand, weathered biotite flakes are fragile unlike gold. It is known as "cat gold".
Placer gold has been mined in many rivers in Bulgaria. Traces of ancient gold mining still exist in Strandzha Mountain. In the area of the village of Kalovo, the sediments of the river Suhata reka were completely overhauled, and the old terraces of River Mladezhka are now large pits. The area of the village Slivarovo is also suitable.

Petya Yordanova


[color=red]Upon request, the Natural History Museum in Burgas may arrange school trips in Strandzha Mountain with professional geologist as a guide for gold panning.[/color]

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