Philadelphia is the largest city in Pennsylvania and the sixth most populous city in the United States. It is the fifth largest metropolitan area and fourth largest urban area by population in the United States, the nation's fourth largest consumer media market as ranked by the Nielsen Media Research, and the 49th most populous city in the world. It is the county seat of Philadelphia County. A popular nickname for Philadelphia is The City of Brotherly Love. The city is recognized as a strong candidate global city. In 2005, the population of the city proper was estimated to be over 1.4 million, while the Greater Philadelphia metropolitan area, with a population of 5.8 million, was the fifth-largest in the United States. A commercial, educational, and cultural center, the city was once the second-largest in the British Empire (after London), and the social and geographical center of the original 13 American colonies. During the 18th century, it eclipsed New York City in political and social importance, with Benjamin Franklin taking a large role in Philadelphia's early rise to prominence. It was in this city that some of the ideas, and subsequent actions, gave birth to the American Revolution and American Independence, making Philadelphia a centerpiece of early American history. It was the most populous city of the young United States and served as the the nation's second capital in 1774.

Emeralds

Emeralds, like all colored gemstones, are graded using four basic parameters – the four Cs of Gemstones: Color, Cut, Clarity and Crystal. The last C, crystal is a synonym that begins with C for transparency or what gemologists call diaphaneity. Before the 20th century, jewelers used the term water as in a gem of the finest water to express the combination of two qualities, color and crystal. Normally, in the grading of colored gemstones, color is by far the most important criterion. However, in the grading of emerald, crystal considered a close second. Both are necessary conditions. A fine emerald must possess not only a pure verdant green hue as described below, but also a high degree of transparency considered a top gem. In the 1960s, the American jewelry industry changed the definition of emerald to include the green vanadium-bearing beryl as emerald. As a result, vanadium emeralds purchased as emeralds in the United States recognized as such in the UK and Europe. In America, the distinction between traditional emeralds and the new vanadium kind reflected in the use of terms such as Colombian Emerald. Scientifically speaking, color divided into three components: hue, saturation and tone. Yellow and blue, the hues found adjacent to green on the spectral color wheel, are the normal secondary hues found in emerald. Emeralds occur in hues ranging from yellow-green to blue-green. The primary hue must be green. Only gems that are medium to dark in tone considered emerald. Light-toned gems known by the species name, green beryl. In addition, the hue must be bright (vivid). Gray is the normal saturation modifier or mask found in emerald. A grayish green hue is a dull green. Emerald tends to have numerous inclusions and surface breaking fissures. Emerald graded by eye. Thus, if an emerald has no visible inclusions to the eye it considered flawless. Stones that lack surface breaking fissures are extremely rare and therefore almost all emeralds are treated, oiled, to enhance the apparent clarity. Eye-clean stones of a vivid primary green hue with no more than 15% of any secondary hue or combination of a medium-dark tone command the highest prices.6 This relative crystal non-uniformity makes emeralds more likely than other gemstones to be cut into cabochons, rather than faceted shapes.