Cairo is located on the banks and islands of the Nile River in the north of Egypt, immediately south of the point where the river leaves its desert-bound valley and breaks into two branches into the low-lying Nile Delta region. Cairo is the capital and largest city of Egypt and on the African continent. It is the Arab World's largest and Africa's second most populous city. While Al-Qahirah is the official name of the city, in Egyptian Arabic it is called by the dialect's name for the country, transliteration: Masr. Cairo was founded by the Fatimid caliphs as a royal enclosure. It replaced Fustat as the seat of the government. It later came under the Mamluks, was ruled by the Ottomans 1517 to 1798, and briefly occupied by Napoleon. Muhammad Ali of Egypt made Cairo the capital of his independent empire from 1805 to 1882, after which the British took control of it until Egypt attained independence in 1922. Cairo has a population of about 6.8 million people, according to the 2006 population census. The number of inhabitants was about a million higher at the time of the census, but this was adjusted downwards on the 17th of April 2008 when the new governorate of Helwan was created from parts of a.o. Cairo governorate. Cairo's metropolitan area has a population of about 17.8 million people. Cairo is the sixteenth most populous metropolitan area in the world. It is also the most populous metropolitan area in Africa.

Rubies

The ruby is a pink to blood-red colored gemstone, a variety of the mineral corundum. The red color caused mainly by the presence of the element chromium. Its name comes from ruber Latin for red. Other varieties of gem-quality corundum called sapphires. The ruby considered one of the four precious stones, together with the sapphire, the emerald, and the diamond. All natural rubies have imperfections in them, including color impurities and inclusions of rutile needles known as silk. Gemologists use these needle inclusions found in natural rubies to distinguish them from synthetics, simulants, or substitutes. Usually the rough stone heated before cutting. Almost all rubies today treated in some form, with heat treatment being the most common practice. However, rubies that are completely untreated but still of excellent quality command a large premium. The Price of rubies primarily is by color. The brightest and most valuable red called pigeon blood red, commands a huge premium over other rubies of similar quality. After color follows clarity: similar to diamonds, a clear stone will command a premium, but a ruby without any needle-like rutile inclusions may indicate that the stone been treated. Cut and carat also determine the price. In the evaluation of colored gemstones, color is the single most important factor. Color divides into three components, hue, saturation and tone. Hue refers to color as we normally use the term. Transparent gemstones occur in the following hues: red, orange, yellow, green, blue, violet, purple and pink are the spectral hues. The first six are spectral hues; the last two are modified spectral hues. Purple is a hue that falls halfway between red and blue. Pink is a paler shade of red. In nature there are rarely pure hues so when speaking of the hue of a gemstone we speak of primary and secondary and sometimes tertiary hues. In ruby the primary hue must be red. All other hues of the gem species corundum called sapphire. Ruby may exhibit a range of secondary hues. Orange, purple, violet and pink are possible.