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Seeing In The Dark

In the movies, there are all sorts of nasty things that can see perfectly well in the dark. More realistic movies also boast their share of 'beasts' that can see in the dark. Who could forget the eerie sight of FBI trainee Clarice Starling being stalked in the pitch-dark basement of the psychotic killer's torture house? The insecurity and near ...

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SeeingInTheDark
Engineering

Big Boom

They sound like thunder, but they're not. They're sonic booms, concentrated blasts of sound waves created as vehicles travel faster than the speed of sound. To understand how the booms are created, ... Continue reading

BigBoom
Engineering

For Want Of An O-Ring

Who can forget the Challenger disaster of 1986, the culprit, a failed O-ring. But what exactly is an O-ring and how did it cause the destruction of this space shuttle? When surfaces are flat, gaskets ... Continue reading

ForWantOfAnORing
Physics

Delivered by TIR

The content of this article has been delivered to you via internet fiber-optic links. Today most phone conversations, fax transmissions and almost all internet and email traffic travel at the speed of ... Continue reading

TIR
Geology

Man Made Clouds

There are many different types of clouds in the sky, but did you know that some of them are man-made? 'Contrails' are the long, thin clouds that are left by airplanes as they fly past. Contrails ... Continue reading

ManMadeClouds

Metamorphic Rock

MetamorphicRockThere are three rock types on earth, named according to how the rock is formed. Igneous rock forms as it cools to a solid from molten rock. Sedimentary rock is formed from the consolidation of particles that come from other rock that has been weathered and eroded. Metamorphic rock forms when solid rock is altered by intense heat, pressure, or both. The original, unaltered rock is called the 'parent' rock and can be igneous, sedimentary, or metamorphic in origin.

Metamorphism (from the Greek terms 'meta'--to change, and 'morph'--form) can occur in several ways. 'Regional' metamorphism occurs when huge masses of magma are intruded deep within the crust over a wide area. The intrusion often occurs along converging (colliding) or diverging plate boundaries and causes high heat and high pressures. Superheated fluids circulating through rock pores and fractures are also involved in regional metamorphism. The fluids can come from the magma, from groundwater, or perhaps even from sea water entering at the plate boundary. These fluids cause 'metasomatism'--chemical changes in the rocks due to the exchange of elements between the fluids and the heated rocks. Rocks may be so altered that the parent rock cannot be identified.

'Contact' metamorphism occurs over a fairly small area when veins of magma are intruded in the upper crust. Pressures do not increase much, but high heat can cause recrystallization. 'Dynamic,' or 'cataclastic', metamorphism often occurs along faults. The rocks can be ground to a powder or may be altered by sudden high pressures at low temperatures. 'Impact' metamorphism occurs around meteor craters. The sudden impact pressure alters surface minerals producing those usually found only in the lowermost crust. Some useful metamorphic rocks are marble and slate. Profitable metal mines (copper, iron, etc.) are often found in zones of contact metamorphism or along the outer boundaries of regionally metamorphosed rock. Some other common metamorphic rocks are quartzite, micas, schist, and gneiss.