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Porphyry is a groundmass, which is a rock "structure". Its chief characteristic is a large difference between the size of the tiny matrix crystals and other much larger crystals. Porphyries may be aphanites or phanerite s, that is, the groundmass may have invisibly small crystals, like basalt, or the individual crystals of the groundmass may be easily distinguished with the eye, as in granite. Many types of igneous rocks may display porphyry.

1 Formation

Porphyry deposits are formed when a column of rising magma is cooled in two stages. In the first stage, the magma is cooled slowly by contact with overlying rocks, creating the large crystal grains, with a diameter of 2 mm or more. In the final stage, the magma is cooled rapidly as it erupts from a volcano, creating small grains that are usually invisible to the unaided eye. The cooling also leads to a separation of dissolved metals into distinct zones. This process is one of the main reasons for the existence of rich, localised metal ore deposits such as those of gold, copper, molybdenum, lead, tin, zincZinc is a chemical element in the periodic table that has the symbol Zn and atomic number 30. Notable characteristics Zinc is a moderately reactive metal that will combine with oxygen and other non-metals, and will react with dilute acids to release hydro and tungstenThis article is about the chemical element. Tungsten may also refer to the Tungsten Handheld PDA. Tungsten (formerly Wolfram is a chemical element in the periodic table that has the symbol W ( L. Wolframium and atomic number 74. A very hard, heavy, steel-.

2 Porphyry in history

In the ancient world, porphyry was quarried only in EgyptAncient Egypt (also see Ancient Egyptian) was the civilization of the Nile Valley between about 3000 BC and the conquest of Egypt by Alexander the Great in 332 BC. As a civilization based on irrigation it is the quintessential example of an hydraulic empi and was reserved for the use of the PharaohThis article refers to the historical Pharaoh. For Pharaoh in the Book of Abraham, see Pharaoh (Book of Abraham). Pharaoh Standard Hebrew Paro Tiberian Hebrew Paroh is a title used to refer to the kings (of godly status) in ancient Egypt. See History of E. In the Byzantine EmpireThe Byzantine Empire or Eastern Roman Empire was the eastern section of the Roman Empire, with its capital at Constantinople (modern Istanbul), which remained in existence after the fall of Rome in the 5th century. The Byzantine period is usually consider, the palace room reserved for royal births was lined with porphyry, and the emperors born in this room were referred to as porphyrogenitus ('born in the purple').