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ACT Science Free Online Practice Test 1

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 Metamorphic rocks form when temperature and/or pressure cause changes in preexisting rock. Figure 1 shows the temperature and pressure conditions in which certain facies (categories of metamorphic rocks) are formed.

Figure adapted from Sheldon Judson, Marvin Kauffman, and L. Don Leet, Physical Geology . ©1982 by Prentice-Hall, Inc.
  A rock’s metamorphic grade (a measure of the intensity of metamorphism) is classified on a scale of low (very similar to the original rock) to high (very different from the original rock). Table 1 lists the grades of Facies A–G from Figure 1. Figure 2 shows characteristic minerals that may be present in rocks of a given grade.
   table 1  
A     low
B     low
C     low to medium
D     low to medium
E     medium
F     medium to high
G     high
*Metamorphic grade is a measure of the intensity of metamorphism.

Figure 2 adapted from Frank Press and Raymond Siever, Earth . ©1986 by W. H. Freeman and Co.
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