Question

recrystallization of pre - existing minerals—unusually high temperatures can also cause the recrystallization of minerals. for example, a limestone (or dolostone) can recrystallize to produce calcitic (or dolomitic) marble (fig. 6.2). sandstone can also recrystallize, producing quartzite (fig. 6.3).

q6.1 (ref. figure 6.2) (a) judging from the changes that are evident in these two before - and - after illustrations, do you suppose the relative age of calcitic marble could be determined from its fossil content as can be done with fossiliferous limestone? (b) why or why not?

q6.2 (ref. figure 6.2b) account for the straight boundaries (flat surfaces) of individual crystals at the fracture surface of the calcitic marble. hint: check out the properties of calcite in table 3.3 on page 61.

q6.3 (ref. figure 6.3) explain the difference between the fracture surface of quartz sandstone and that of quartzite. hint: check out the properties of quartz in the lower one - half of table 3.3 on page 60.

figure 6.2 a fossiliferous limestone (a) can recrystallize to form the metamorphic rock calcitic marble (b). notice the several changes that are apparent in b. (these are magnified views of sawed surfaces that are in the plane of the page.)

figure 6.3 sandstone (a) can recrystallize to form the metamorphic rock quartzite (b). ghosts of original quartz sand grains (see the cloudy centers of crystals) might be apparent in quartzite. (these are magnified views of sawed surfaces that are in the plane of the page.)

construction of the washington monument in the 19th century marked the change from sandstone to marble as the stone of choice in buildings and monuments of washington, d.c. this landmark was begun in 1848 using marble from the texas, maryland quarry, but a lack of funds halted construction in 1854. interest was rekindled in 1879, and construction was resumed with lee marble. but lee marble proved to be too costly, so marylands cockeysville marble was used from 1880.

building stones of our nations capital is a pamphlet produced by u.s. geological survey and distributed by u.s. government printing office: 1998—673 - 048 / 20116.

Explanation:

Q6.1 (A)

No, the age of cal - citic marble cannot be determined from its fossil content compared to fossiliferous limestone.

Q6.1 (B)

During recrystallization, fossils in limestone are destroyed or altered beyond recognition, so fossils cannot be used for age - determination in calcite marble.

Q6.2

Calcite has cleavage planes. When the calcite marble fractures, the breakage occurs along these pre - existing cleavage planes, resulting in straight boundaries of individual crystals at the fracture surface.

Q6.3

Quartz sandstone has a matrix between quartz grains and fractures irregularly around the grains. Quartzite is a metamorphic rock with intergrown quartz crystals. Its fracture surface is more regular and smooth as it breaks through the intergrown crystals rather than around grains in a matrix.

Answer:

Q6.1 (A): No
Q6.1 (B): Fossils are destroyed or altered during recrystallization.
Q6.2: Calcite has cleavage planes, and fractures occur along them.
Q6.3: Quartz sandstone fractures around grains in a matrix, while quartzite fractures through intergrown crystals, resulting in a smoother and more regular fracture surface.