friday december 10, 2010

FridayDecember 10, 2010(Intro to Minerals;

Properties of Minerals)

The Launch PadFriday, 12/10/10

What’s the difference between a mineral and a

rock?A mineral is a naturally occurring solid chemical substance that is formed through geological processes, and

that has a characteristic chemical composition, a highly ordered atomic

structure, and specific physical properties.A rock is an mixture of minerals and/or mineraloids and does not have a

specific chemical composition.

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MineralsThe Building

Blocks of Rocks(Textbook, Chapter 2)

Minerals - The Building Blocks of Rocks o Recall from chemistry that elements

and compounds are collectively known as “substances.”

o Elements bond together to form “compounds.”

o Elements and compounds have a definite chemical formula.o ex.) Elements: Na is sodium and Cl is

chlorine.o ex.) Compound: NaCl is sodium

chloride, or common table salt.o In geology, we normally call rocky

elements and compounds “minerals.”o Sodium chloride is called rock salt, or

halite, when we’re discussing minerals.

Figure 2.2

Minerals - The Building Blocks of Rocks A mineral is a naturally occurring solid chemical

substance that is formed through geological processes and that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical

properties.By comparison, a rock, which we will study later, is

an mixture of minerals and/or mineraloids and does not have a specific chemical composition.

Minerals range in composition from pure elements and simple salts to very

complex silicates with thousands of known forms.The study of minerals is called mineralogy.

Figure 2.3

Minerals - The Building Blocks of Rocks A mineral is naturally

occurring, inorganic, solid in phase, possesses an

orderly internal structure of atoms, and has a

definite chemical composition.

Mineraloids, on the other hand, lack an orderly

internal structure.

Lechatelierite

Fluorite

Minerals - The Building Blocks of Rocks Physical properties

of minerals Streak

When you rub a mineral on a flat surface, the color of the powder left behind on the

streak plate is the mineral's streak.

The streak and color of some minerals are the same. For others, the streak may be

quite different from the color.

Although the color of a mineral may not be very helpful in identification, the streak, which is the color of the

powered mineral, can be very useful.

Minerals - The Building Blocks of Rocks

Physical properties of minerals

HardnessMineral hardness is based on

the ability of one natural sample of matter to scratch

another.Diamond is the hardest

known naturally occurring substance, whereas talc is the

least hard.



HardnessThe hardness of a material is

measured against the Mohs scale by finding the hardest material that

the given material can scratch, and/or the softest material that can scratch the given material.

For example, if some material is scratched by apatite but not by

fluorite, its hardness on the Mohs scale would fall between 4 and 5.

Figure 2.13

Mohs Scale of Hardness



CleavageIn mineral terms, cleavage describes how a crystal breaks when subject to

stress on a particular plane.If part of a crystal breaks due to stress and the broken piece retains a smooth plane or crystal shape, the mineral has

cleavage.A mineral that never produces any

crystallized fragments when broken off due to stress has no cleavage.

Three Examples of Cleavage – Halite, Calcite, and Fluorite

Figure 2.15 B

Cleavage


of minerals Habit

Mineral habit is the shape of how a mineral tends to form.

Types of mineral habits include columnar, blocky,

acicular (needle-like), granular, lamellar or foliated

(sheets easily split apart), botryoidal (like a bunch of

grapes), fibrous, radiating, or dendritic (like a fern).

The mineral quartz often exhibits good crystal shape

Pyrite (fool’s gold) has two common crystal forms

Figure 2.11

Figure 2.12Abladed habit

Figure 2.12Bprismatic habit

Figure 2.12Cbanded habit

Figure 2.12Dbotryoidal habit


of minerals Luster

The luster of a mineral is the way its surface reflects light. In simplest

terms, minerals have a metallic or non-metallic luster. A metallic luster is a shiny, opaque appearance similar to

a bright chrome bumper on an automobile. Other shiny, but

somewhat translucent or transparent lusters (glassy, adamantine), along

with dull, earthy, waxy, and resinous lusters, are grouped as non-metallic.

The freshly broken sample of galena (right) displays a metallic luster, while the sample on

the left is tarnished and has a submetallic luster.



ColorThe color of a mineral is one of its most

obvious attributes, and is one of the properties that is always given in any

description. Color results from a mineral’s chemical composition,

impurities that may be present, and flaws or damage in the internal

structure. Color in minerals is caused by the absorption, or lack of absorption, of

various wavelengths of light.

Minerals - The Building Blocks of Rocks Physical properties of

minerals Fracture

Fracture is a description of the way a mineral tends to break. It is different

from cleavage and parting, which are generally clean flat breaks along specific directions.

Different minerals will break in different ways and leave a surface that can be described in a recognizable way. Is the broken area smooth?

Irregular? Jagged? Splintery? These are some of the ways of describing fracture. Although many

minerals break in similar ways, some have a unique fracture and this can be diagnostic.


of minerals Fracture

The most common fracture type is conchoidal. This is a smoothly curved fracture that is familiar to

people who have examined broken glass. Sometimes described as

a clam-shell fracture. Quartz has this fracture type and almost all

specimens that have been broken, demonstrate this fracture type very

well.

Conchoidal Fracture

Figure 2.16



Another common type is subconchoidal. Similar to conchoidal, just not as curved, but still smooth. Andalusite can show this

type.



Uneven is a type that is basically self

explanatory. It is a common type that is found in anhydrite.



Jagged fractures have sharp points or edges that

catch on a finger that's rubbed across the surface.

Usually this indicates a metal such as copper , a

metal alloy or some sulfides or oxides.



Splintery is a fracture type that occurs in fibrous or finely acicular minerals and in minerals that have

a relatively stronger structure in one direction than the other two. Chrysotile serpentine is a typical mineral with splintery fracture, and kyanite is an example of a

non-fibrous mineral that has this fracture.



Earthy is a fracture that produces a texture similar to broken children's clay.

It is found in minerals that are generally massive and loosely consolidated such

as limonite.

friday december 10, 2010

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