Download GL 121: Answer Sheet for Lab 1

Rock Forming Minerals
Minerals are important because every inorganic item that has been manufactured originated
from a mineral. Minerals are inorganic, naturally occurring substances that have a characteristic
chemical composition, distinctive physical properties, and crystalline structure. Crystalline
structure is an orderly three-dimensional arrangement of atoms or molecules, and materials with
crystalline structure form crystals. A few “minerals” do not have crystalline structure and so
don’t form crystals – these are called mineraloids. Most mineral crystals occur in rocks, which
are simply defined as an aggregate of one or more minerals. In this lab, we will investigate some
rock-forming minerals. In this lab, the minerals are organized based on their chemical
composition. The most common are listed below.
Classification Scheme for Minerals (Groups)
□ Elements – minerals composed of a single element, such as Gold (Au), Silver (Au) –
usually metals or metalloids
□ Sulfides & related compounds – minerals that contain sulfur as S or S2
□ Haloides – minerals that contain halides such as chlorine (Cl), fluorine (F): halite is the
mineral that is mined to make table salt, and is represented by NaCl
□ Oxides – minerals that contain oxygen (O, as in Rutile TiO; O2, O3, O4) & Hydroxides –
minerals that contain (OH)
□ Carbonates – minerals containing CO3
□ Sulfates – minerals that contain sulfur as SO4
□ Phosphates – minerals that contain phosphorus (P) as PO4
□ Silicates – minerals that contain silica in the form of SiO2,SiO4, Si2O6, Si3O8, Si3O10, or
any combination of Silicon (Si) and Oxygen (O)
□ Organic – often not “true” minerals, as minerals must be inorganic. This category
includes Amber (fossil tree sap), fossils, shell material, pearls, coral, bone, etc.
Characteristics of Minerals
Color is a mineral’s most easily observed property – but is not really all that useful for
identifying minerals. Many minerals are produced in a range of colors, based on the impurities
that are included in their atomic makeup. Minerals also vary in clarity; they may be transparent
(clear, like window glass), translucent (“foggy”), or opaque (not possible to see through).
Crystal form describes the three-dimensional geometric shape that a mineral assumes. Often,
we can infer the crystal form if only a portion of the shape is visible or the crystal is broken.
Perfect crystals only grow when they are totally unrestricted during growth. Most of our lab
specimens will not be perfect crystals, but we can still determine their identity by performing
other tests. Minerals are said to be cryptocrystalline when the crystals the specimen is composed
of are too small to be seen without magnification.
Hardness is a measure of resistance to scratching. A harder surface will scratch a softer one. A
quantitative scale of hardness was developed by Frank Mohs where the softest mineral (talc) has
a hardness of 1 and the hardest mineral (diamond) has a hardness of 10. Higher numbered
minerals will scratch lower numbered ones. Hard minerals can scratch glass and soft minerals
cannot.
Mohs Scale of Hardness
Hardness of some common objects:
HARD
10 – Diamond
9 – Corundum (sapphire, ruby)
8 – Topaz
7 – Quartz
6 – Orthoclase or Feldspar
5 – Apatite
SOFT
4 – Fluorite
6.5 Streak Plate
5.5 Glass, masonry nail, knife blade
4.5 Wire (iron) nail
3 – Calcite
3.5 Copper wire or coin (penny)
2 – Gypsum
2.5 Fingernail
1 – Talc
Streak is the color of a substance after it has been ground or scratched to make a fine powder.
The easiest way to do this is by scratching the mineral across a plate of unglazed porcelain.
Some minerals are hard enough that it can be difficult to get a good streak. If you can’t get a
good streak, test the hardness – if it is greater than 7, the white streak you see is likely from the
streak plate and not the mineral.
Luster is a description of how light reflects from the surface of an object (such as a mineral).
Luster can be described as “metallic” or “non-metallic”. The luster of “nonmetallic” minerals
can be described in further detail as: “vitreous” – resembling the luster of freshly broken glass;
“waxy” – resembling the luster of a candle; “pearly” – resembling the luster of a pearl; “satiny” –
resembling the luster of satin or silk cloth; “earthy” – lacking reflection, completely dull, like dry
soil; “greasy” resembling the luster of grease, oily; or “porcelaneous” – resembling the luster of
porcelain.
Cleavage is the tendency for some minerals to break (cleave) along flat, parallel surfaces
(cleavage planes). The cleavage planes are parallel surfaces of weak chemical bonding
(attraction) between repeating, parallel layers of atoms in a crystal, and more than one set of
cleavage planes can be present in a crystal (as many as 6). Fracture refers to any break in a
mineral that does not occur along a cleavage plane – fractures are not normally flat and never
occur in parallel sets.
Magnetism can influence some minerals. Test for magnetism by putting a magnet near the
mineral. If it attracts, it is magnetic, and you may be able to attract small metal objects with it
(such as paperclips). This is a special property of some minerals.
Reaction with hydrochloric acid is different among minerals. All carbonate minerals (those
with carbonate, CO3) will effervesce (fizz) when acid is dropped onto them. Some minerals
(such as Dolomite) will only react once powdered (such as with a steel nail). We will not
perform an acid test in this lab.
* missing information is intentional.
white
white
7
non-metallic
non-metallic
non-metallic
Garnet
Gypsum
Halite
7
non-metallic
Olivine
1
non-metallic,
greasy.
Talc
white
whtie
greybrown
Some Uses
Plaster of Paris, wallboard, drywall, art
sculpture medium (alabaster).
Used as an abrasive, on sandpaper, as a
gemstone (birthstone for January).
Used to make ceramics, glass, enamel, soap,
false teeth, scouring powders.
Gemstone (peridot) for August. Ore of
magnesium metal.
Used for fire-resistant tiles, rubber, paint.
Ore of iron for steel, brass, bronze, tools,
vehicles, nails and bolts, bridges, etc.
Red pigment. Ore of iron for steel tools,
vehicles, nails and bolts, bridges, etc.
Color white, gray, pale green or brown. No cleavage. Feels
greasy or soapy. Very soft.
Used for talcum powder, facial makeup,
ceramics, paint, sculptures.
Usually colorless, white or gray but uncommon varieties occur Used as an abrasive, used to make glass,
in all colors. Transparent to translucent. No cleavage
gemstones (Purple - Amythyst - Februrary,
(concoidal fracture) Forms hexagonal pyramids and prisms. Orange -Citrine)
Color brass yellow ("fools gold"). Opaque. Tarnishes brown. Ore of sulfur, for sulfuric acid, explosives,
Forms cubes or eight-sided polygons. No cleavage.
fertilizers, pulp processing, insecticides.
Color silvery-gray, black or brick red. Tarnishes red. Opaque.
Soft (earthy) and hard (metallic) varieties have same streak.
Forms thin crystals or is massive.
color silvery gray to black. Opaque. Forms 8 sided
polyhedrons. Tarnishes gray. No cleavage. Magnetic?
Color black, green-black or brown-black. Cleavage excellent.
Can split into thin, flexible sheets.
Color pale or dark olive-green to yellow, or brown. Forms
short crystals that may resemble sand grains. Concoidal
fracture. Cleavage absent.
Colorless, white, yellow, brown, blue or red. Transparent to
Table salt, road salt; used in water softeners
translucent. Forms cubes, but may be massive. Cleavage is
and as a preservative. Sodium Ore.
___________________________. Salty taste (don't lick!)
Color orange, brown, white, green or pink. Cleavage excellent
in two directions at nearly 90degrees.
Color usually red, black, or brown; sometimes yellow, green,
pink. Forms 12 sided polyhedron. No cleavage. Translucent
to opaque.
Colorless, white or gray. Forms blade shapes or needles.
Transparent to translucent. Very soft. Cleavage good.
Usually colorless, white or yellow, but may be green, brown, or
Used to make antacid tablets, fertilizer,
pink. Opaque or transparent. Excellent cleavage in 3
cement; ore of calcium.
directions not at 90 degrees. Reaction to HCl?
Distinctive Properties
* some spaces have been left blank where you are required to determine these properties during lab.
7
non-metallic,
greasy.
Quartz
6 - 6.5
2.5 - 3
non-metallic
Mica (biotite)
Pyrite
6
Metallic
Magnetite
(Fe3O4)
1.5 - 6
metallic or nonmetallic
Hematite
(Fe2O3)
2
white
6
non-metallic
Feldspar
white
white
Streak
non-metallic
Hardness
Calcite
Luster
Properties of 12 Rock-Forming Minerals
Answer Sheet for Lab 2
Name: _______________________
Rock-Forming Minerals
Date: _______________________
Instructions: Please fill in your answers for the lab on this lab sheet. No red pens or markers.
--------------------------------------------------------------------------------------------------------------------The minerals in this lab are labeled by name. Your teacher will instruct you to investigate each
of the minerals. The objective of today’s lab is to learn some of the most common minerals, and
how to identify them.
Define Mineral: (hint – there are 5 characteristics to a mineral)
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Define Rock:
______________________________________________________________________________
Mineral ID Lab:
Galena
PbS
Pyrite
FeS2
Sulfur
S
Do a streak test for each of these minerals. What are their streak colors?
Galena
_________________
Pyrite
_________________
Sulfur
_________________
What kind of luster do they have? ________________________________________________
Do these minerals have cleavage or fracture? Write next to mineral name above.
What is the hardness of these minerals?
Galena
_________________
Pyrite
_________________
Sulfur
_________________
Fluorite
CaF2
Halite
NaCl
Copper
Cu (native element)
Do a streak test for each of these minerals. What are their streak colors?
Fluorite
_________________
Halite
_________________
Copper
_________________
Do these minerals have cleavage or fracture? Write next to mineral name above.
What kind of luster do they have? ________________________________________________
What is the hardness of these minerals?
Fluorite
_________________
Halite
_________________
Copper
_________________
Hematite
Fe3O4
Magnetite
Fe2O3
Quartz
SiO2
Which of these minerals is magnetic?
_________________
What kind of luster do they have? ________________________________________________
Do these minerals have cleavage or fracture? Write next to mineral name above.
Do a streak test for each of these minerals. What are their streak colors?
Hematite
_________________
Magnetite
_________________
Quartz
_________________
What is the hardness of these minerals?
Hematite
_________________
Magnetite
_________________
Quartz
_________________
Calcite
CaCO3
Olivine
(Mg,Fe)2[SiO4]
Kaolin
Al2Si2O5(OH)4
Do a streak test for each of these minerals. What are their streak colors?
Calcite
_________________
Olivine
_________________
Kaolin
_________________
What kind of luster do they have? ________________________________________________
Do these minerals have cleavage or fracture? Write next to mineral name above.
What is the hardness of these minerals?
Calcite
_________________
Olivine
_________________
Kaolin
_________________
Gypsum
CaSO4·2H2O
Talc
Mg3[(OH)2|Si4O10]
Graphite
C (considered a native element made of Carbon)
Do a streak test for each of these minerals. What are their streak colors?
Gypsum
_________________
Talc
_________________
Graphite
_________________
What kind of luster do they have? ________________________________________________
What is the hardness of these minerals?
Gypsum
_________________
Talc
_________________
Graphite
_________________
Do these minerals have cleavage or fracture? Write next to mineral name above.
Silicates – Bonus Impress Me Questions!
Augite
(Ca,Mg,Fe)[(Si,Al)2O6]
Horneblende Ca2Na(Mg,Fe2)4(Al,Fe3)[(Si,Al)4O11][OH]2
Biotite
Muscovite
K(Mg,Fe)3[(OH,F)2|AlSi3O10]
KAl2[(OH,F)2|AlSi3O10]
Potassium Feldspar K[AlSi3O8]
Plagioclase Feldspar nNa[AlSi3O8] + nCa[Al2Si2O8]
Garnet
Kyanite
Olivine
Talc
Quartz
Fe3Al2[SiO4]3
Al2[O|SiO4]
(Mg,Fe)2[SiO4]
Mg3[(OH)2|Si4O10]
SiO2
The silicates are a very diverse and complex group of minerals. What do they ALL have in
common? _____________________________________________________________________
Can you distinguish differences between the minerals in the mica group by visually
observing them? What about their chemistry causes this difference? (I told you about the
visual differences!)
______________________________________________________________________________
Summary – Impress Me Some More!
Which group would ICE (yes, the crystal form of water) be a part of? _________________
Organic materials that are often considered minerals (but are not) are coal and amber.
Why aren’t they minerals? (hint: what criteria of “mineralness” do they not meet?)
______________________________________________________________________________
______________________________________________________________________________
Is a shell a mineral? Shells are often made of aragonite (like snails and clams) or calcite
(sea urchins). Why or why not? ________________________________________________
Look at the following samples, and fill in the chart for them below. Using the charts in the
introduction and your notes taken during lab, identify the minerals.
#
Luster
Hardness
Cleavage
Color/Streak
Special
Identification
1
2
3
* For luster, choose metallic, glassy, earthy, or greasy.
* For streak, report color that is found when the mineral sample is rubbed on a porcelain plate.