ANSWERS TO “TEST YOUR KNOWLEDGE” ON PAGE 34 Answers:


1. The answer is choice “b” or “Olivine and anorthite.” Olivine [(Mg, Fe)2SiO4] is the first mineral to crystallize in a cooling mafic magma from the ferromagnesian series. Similarly, anorthite [CaAl2Si2O8] is the calcium-rich variety of plagioclase feldspar that crystallizes first in a cooling mafic magma.


Orthoclase [KAlSi3O8] and quartz [SiO2] are products of late stages of magmatic crystallization. Olivine and anorthite are generally found in mafic igneous rocks, whereas orthoclase and quartz are commonly encountered in felsic igneous


rocks. Olivine and quartz do not usually occur together.


Choice “d” may be found at celebration parties where a variety of adult beverages are consumed and when one steps on the dog’s tail.


2. The answer is choice “c” or “A linkage formed by sharing electrons.” It constitutes the strongest type of chemical bond. Choice “a” pertains to ionic bonding. Choice “b” describes “van der Waal’s bonding.”


3. The answer is choice “a” or “Propane.”


Ethane [C2H6] and butane [C4H10] are also part of the alkane family of hydrocarbons, along with methane [CH4], the simplest member of the family.


I remember “stinkane” when I lived close to an oil refinery.


4. The answer is choice “b” or “The stratigraphic section is inverted.” Kimmeridgian and Campanian strata are upper Jurassic and upper Cretaceous, respectively. Since the Kimmeridgian rocks overlie the Campanian lithologic units, the section must be inverted.


A nonconformity defines and unconformable surface that separates igneous or metamorphic rocks from overlying sedi- mentary strata. This is not our case here.


Triassic rocks do not apply in our example, since we have only mentioned Jurassic and Cretaceous lithologies as seen in our full-diameter core.


 h


The volume and weight of the block are: v = bcd w = bcdpg


The horizontal stress required to move the block is: h = Fh / cd The coefficient of friction is:


 sn  


 hh


 h:  hh  hh  hh  hh  hh hh h h


This last equation is the answer that we seek and our choice “a.” Thus, the horizontal stress required to move our earth block can be expressed in terms of the length of the block, the density of the rock, the acceleration of gravity, the coef- ficient of friction along the detachment surface and the angle of the sloping surface.


36 TPG • Jan.Feb.Mar 2021 www.aipg.org


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