01 Minerals in Rock

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Copyright © 2016 National Institute of Geological Sciences. All Rights Reserved. Laboratory Exercise 1

National Institute of Geological Sciences Elementary Petrology

MINERALS IN ROCKS

A. Introduction

A rock is basically an aggregate of minerals, mineraloids, and organic fragments, whether only of onekind or several. Hence, even samples with only one mineral are also considered as rocks. However,

minerals in rocks do not always occur as well-formed crystals (like the samples in the Geology 40).

Varying factors (such as temperature and pressure) during rock formation affect the growth of the

mineral constituents. The common rock-forming minerals, though only few in number, may not be easily

identified because they usually (but not always) appear differently in rocks. Aside from not having well-

formed crystal faces, the minerals are commonly small making examination of properties difficult.

In Exercise 1, familiarize yourself with how common rock-forming minerals usually occur in different

kinds of rocks.

The student should be able to:

1. describe the appearance of the minerals in rocks, and;

2. Identify the minerals present in the rocks using their diagnostic properties.

B. Definition of terms

Rock – a consolidated aggregate of one or more minerals, mineraloids, and/or organic materials.

Euhedral – crystal with well-formed faces

Subhedral –

crystal with imperfectly developed faces

Anhedral – crystal without developed faces

Disseminated – scattered; dispersed

Massive – compact crystalline aggregates with no regular form

Cleavable – can be separated along cleavage planes

Irregular grains – anhedral grains

Aggregates/aggregation – crystals as numerous individuals or as clusters

Lath-shaped – rectangular

Striations – parallel lines on crystal face or cleavage plane





C. Activities

1. For each rock sample, describe and identify the minerals present. Make a sketch of each rocksample with a corresponding scale. Label the identified minerals on each drawing. The materials you willneed for this activity are Table 1.1, pencil, ruler, hand lens, pin, pocket knife, water (in atomizer), andacid. Note that the light-colored mineral indicated may include the colorless mineral, if present.

GR16-001 –

1 dark-colored

GR16-002 – 2 light-colored minerals

GR16-003 – 3 light-colored minerals and 1 dark-colored mineral

GR16-004 – dark-colored mineral

GR13-005 – only the mineral big enough to see

GR13-006 – 1 light- colored mineral

GR13-007 – 1 light- colored mineral

GR13-008 – 2 distinct minerals

GR13-009 – 2 light-colored minerals




GR13-013 – 1 dark-colored mineral

GR13-014 –

1 light-colored mineral

GR13-015 – 2 light-colored minerals and 2 dark-colored minerals

GR13-016 – 1 dark-colored mineral

GR13-017 – 1 light colored mineral


GR16-019 – 1 light colored mineral






Name: _______________________________ Section: ________________ Date: ___________

Table 1.1.

Sketch: Minerals present:









Table 1.1.










3. Summarize in Table 1.2 the characteristics of common rock-forming minerals as you haveobserved them in rocks. An example (Quartz) is filled in below.

Table 1.2. Usual characteristics of minerals in rocks.

Mineral Characteristics

Quartz

- granular- do not show crystal faces- white or colorless, hence may take on the color of the mineral beside it in the

rock





Mineral Characteristics

01 Minerals in Rock

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