2005 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist.

MINERALS AND

CRYSTALGROWTH

EXERCISE1

1 © 2005 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist.No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher.Many elementary geology laboratories do not have microscopes for the freshman students, but this exercise may be presented in the form of a demonstration using an overhead pro- jector for magnification.Procedure

• Melt a small amount of thymol in a petri dish.
• Place the melt in the overhead projector and let it cool. Add a few seed crystals

(grains).

• Have students work “Slow Cooling With ‘Seed’Crystals” in the manual (p. 8) from

their observations of this melt.Points to Emphasize

• Crystals grow from material being added to the surface rather than by internal ex-

pansion.

• Angles between crystal faces remain constant through the entire period of growth,

regardless of crystal size.

• Where space is limited, crystals grow in an interlocking manner.
• Growth of crystals in 3-D. This can be effectively demonstrated by changing the

focus to view the top of the large crystals (crystals form an octahedron).

• Crystal size is greatly influenced by rate of growth. Compare the size of crystals in

the center of the dish, where cooling was slow, with the size of those near the edge, where cooling was fast.

• Obtain pieces of granite. Have the students examine the granite and sketch its tex-

ture. Compare the texture of granite with the texture of the crystallized thymol.(Students will probably need help with this, so make a sketch on the board if necessary).(Exercises in Physical Geology 12e Kenneth Hamblin, James Howard) (Solution Manual all Chapters) 1 / 4

Answers to Problems, p. 8

• Growth of Crystals from a Melt

Slow Cooling

2. Growth lines of a crystal are parallel to crystal faces: Outlines of

crystals (grains) in an aggregate are irregular and conform to the space available during crystallization.

• Initiates crystallization.
• The textures are similar.

Slow Cooling vs. Rapid Cooling

• Slow cooling yields large crystals; rapid cooling yields smaller

crystals.

• Interpreting Results of Mineral Growth
• Cavity - well-developed crystal faces free from interference during

growth.

• Two periods of growth are represented because the slender crystals

grew in the space left by the larger crystals.

• Pink crystals grew first, others followed later.
• Irregular crystals grew first, as indicated by their interference with

the gray linear crystals.

• Water from the Salt Lake splashed on the fence and partly evaporat-

ed, causing crystallization.2

MINERALS AND CRYSTAL GROWTH

© 2005 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist.No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. 2 / 4

MINERAL

IDENTIFICATION

EXERCISE2

3 © 2005 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist.No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher.Explain and Demonstrate

• Crystal form
• Cleavage and fracture
• Hardness
• Color and streak
• Miscellaneous physical properties

Points to Emphasize

• Observations of crystal growth and crystal form indicate minerals have a definite

geometric internal structure. A given mineral will have the same interfacial angles. Refer to Figures 2.12–2.16 (pp. 18–24). The value of these photographs depends on how they are used. Insist that students study the photographs careful- ly. A successful technique is to require students to label the most diagnostic phys- ical properties observable in these photographs. This will ensure that they observe and recognize the significant properties rather than the size, shape, and color of specimens. Also, have the students compare a mineral specimen with its corre- sponding photograph and determine which properties are fundamental in mineral identification.

• Cleavage results from weakness in internal structure and should not be confused

with crystal faces. Refer to Figure 2.2 (p. 11 in Lab Man.).

• All physical properties of a mineral are constant (within specific limits), and many

may serve as diagnostic features. The student should learn the diagnostic proper- ties of each mineral.More than 95% of the minerals the students will see in the field will be va- rieties of species shown on pages 18–24.Emphasize that although these minerals appear in various forms, sizes, and colors, each species has definite diagnostic physical properties.The color photographs are to be used only as a reference, not as a key.This is important, because most students have a strong tendency simply to com-pare the specimens with the photos and determine the names of the minerals. 3 / 4

4

MINERAL IDENTIFICATION

© 2005 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist.No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher.Insist that each student record the observable physical properties of the speci- men he works with.This lab work is largely memorization. Remind the students that repetition is the key to learning this material but that there is system and order in the mineral classification chart (Figure 2.11). Suggest that they study the material in the man- ual outside of class and review the samples in the display cases as often as possible.Answers to Problems, p. 25

• A number of physical properties, such as hardness and cleavage, are determined only

from mineral specimens, not from a photograph. Other properties, such as color, size, and shape, which are most obvious on the photographs, may not be diagnostic.

• The angles between similar crystal faces of a specific mineral will be the same re-

gardless of where or when the mineral was formed, even though the overall size or shape of the mineral may vary.

• Crystal form, cleavage, fracture, hardness, density, and streak are generally consid-

ered the most important types of physical properties of minerals when studied in hand specimens.

• A mineral is a naturally occurring, inorganic substance with an orderly internal

atomic arrangement and definite chemical composition that varies only within cer- tain limits.

• Solid solution is the substitution or replacement of one element for another in the

crystal structure of a mineral. Solid solution changes the composition of a mineral but not its internal structure.

• Solid solution is important in feldspars, olivine, pyroxenes, amphiboles, garnets,

and micas.

• A crystal face is the external expression of a mineral’s internal atomic structure. A

cleavage plane is a plane of weakness in the crystalline structure along which the crystal will break.

• Hardness is the degree of resistance of a mineral to abrasion.
• Calcite is the only common mineral that reacts with HCl.
• The typical crystal form of quartz is six-sided prismatic.
• Specimens of microcrystalline quartz are aggregates of microscopic crystals.
• Chert occurs most commonly as nodules in limestone.
• Color, which commonly results from the presence of impurities or inclusions, does

not constitute a fundamental difference in the varieties of the mineral quartz.

• The most diagnostic physical properties of feldspars are: (1) two directions of

cleavage nearly at right angles, (2) hardness of 6, and (3) porcelain luster.

• / 4