What are the Physical Properties of Minerals?

The goal of this lesson is to identify the physical properties of minerals and to introduce the minerals involved in the petrification process of wood.

Minerals

• Minerals are natural solids formed from elements and compounds in the earth’s crust.
• Minerals are inorganic (
• A mineral has definite chemical and physical properties
• The atoms and molecules of most minerals are joined in regular shapes called crystals

Properties to identify minerals:

• Color- Most minerals cannot be identified by color alone, many have the same color and others have many colors.

• Streak- When you rub a mineral on a piece of unglazed tile, it may leave a streak of powder. A mineral may have different colors, but it will always have the same color streak.
• Luster- The luster if a mineral is either shiny or dull. Shiny-metallic luster or glassy and dull-non metallic luster.
• Hardness –The property of a mineral to resist being scratched is called hardness. To determine the hardness one mineral is scratched on another. The Moh’s scale of hardness shows ten minerals that we test for hardness. A mineral can scratch a softer mineral not a harder mineral.

Moh’s Scale of Hardness

	Mineral
Softest- 1	talc
2	gypsum
3	calcite
4	flourite
5	apatite
6	feldspar
7	quartz
8	topaz
9	corundum
Hardest-10	diamond

§ Density- The amount of matter in a given volume.

§ Acid Test- The acid test is used to test mineral for calcium carbonate (CaCO3). Drop a dilute hydrochloric acid on a mineral. If bubbles form, the mineral contains calcium carbonate, such as calcite, dolomite, and malachite.

§ Crystal Shape- There are six basic crystal shapes.

Isometric- crystals with three axes, all perpendicular to one another and all equal in length.

Tetragonal- crystals with three axes, all perpendicular to one another; two are of equal length.

Orthorhombic- crystals with three mutually perpendicular axes, all of different lengths.
Monoclinic- crystals with three axes of unequal lengths, two of which are oblique (that is, not perpendicular) to one another, but both of which are perpendicular to the third.
Triclinic- crystals with three axes, all unequal in length and oblique to one another.
Hexagonal- crystals with four axes. Three of these axes are in a single plane, symmetrically spaced, and of equal length. The fourth axis is perpendicular to the other three.

§ Fracture and Cleavage- The way a mineral splits can be used to identify the mineral. If the mineral splits into smooth and flat pieces it has cleavage, such as calcite. If it splits into uneven pieces it has fracture, such as quartz

Experiment with the Properties of Minerals

Materials:

Quartz Unglazed ceramic tile

Pyrite Medicine dropper

Calcite Eye Protection/ protective clothing

Galena

Hematite

Dilute hydrochloric acid-caustic substance use caution

Procedure:

1. Make observations about the quartz, pyrite, calcite, galena, and hematite. Record data using the chart.
2. Rub the different minerals on an unglazed ceramic tile and record data.
3. Using the medicine dropper and squeeze a few drops on the minerals and record results.

Recording Chart

		Quartz	Pyrite	Calcite	Galena	Hematite
1.	Color
2.	Luster(metallic/nonmetallic)
3.	Does it streak? (yes/no)
4.	Color of streak
5.	Reacted with hydrochloric acid

Types of primary minerals commonly found with fossils

1. . Aragonite. Aragonite (CaCO₃) is a form of calcium carbonate that is fairly unstable and commonly dissolves away. Skeletons made originally of aragonite are commonly recrystallized to calcite and preserved as molds. Aragonite is easy to recognize. It is usually (not always!) milky white and has no luster.

2. Calcite. Calcite (CaCO₃) is the more common form of calcium carbonate. It is more stable than aragonite and therefore does not dissolve as readily. Calcite usually has a grayish color and a slight vitreous (or glassy) luster when found as a skeletal mineral. It can be found as an original skeletal material, or as a recrystallization product.

3. Silica. Silica (SiO₂) is easy to distinguish from the carbonate minerals since it will not react with acid. Skeletons composed of this mineral will commonly have a brown, earthy color, with or without a vitreous luster, and can have a granular texture. Silica is rarely found as an original material and most commonly occurs as a replacement product.

4. Pyrite. Pyrite (FeS₂) or "fools' gold" is a golden colored mineral with a metallic luster and is therefore identified easily. It always appears as a replacement product.

Substance	Formula	Produced	Susceptibilities
aragonite	CaCO3	organically (mollusks, scleractinial corals, algae, some bryozoan, etc., etc.) and inorganically in a large number of environments	acid
calcite	CaCO3	organically (mollusks, brachiopods, echinoderms, tabulate and rugosan corals, etc., etc.) and inorganically in a large number of environments	acid
dolomite	(CaMg)(CO3)2	inorganically, rarely primary - usually produced during diagenesis	acid
apatite	Ca5(PO4)3(OH, F)	organically (chordates, conodonts, brachiopods) and inorganically	acid
opalline silica	SiO2*nH20	organically (some sponges, diatoms, radiolarians, silicoflagellates, etc.) and inorganically	basic conditions
pyrite	FeS2	inorganically, reducing environments with available sulfer and iron	oxidizing conditions
iron oxides and hydroxides	FeO(OH), Fe2O3, other "rusts", etc.	inorganically, oxidizing environments with available oxygen and iron	reducing conditions
gypsum	CaSO4	inorganically, evaporitic environments	can dissolve in water
chitin	polysaccharide carbohydrate	organically (arthropod cuticle)	oxidizing conditions, heat