AY Honors/Rocks & Minerals/Answer Key

1. What is the difference between rocks and minerals?

A mineral is a naturally occurring, inorganic solid with a definite chemical composition and a crystalline structure formed by geological processes. A rock is an aggregate of one or more minerals. (A rock may also include organic remains and mineraloids.) Some rocks are predominantly composed of just one mineral. For example, limestone is a sedimentary rock composed almost entirely of the mineral calcite. Other rocks contain many minerals, and the specific minerals in a rock can vary widely. Some minerals, like quartz, mica or feldspar are common, while others have been found in only one or two locations worldwide.

3. Define and name two examples each (from specimens or pictures) of:

a. Igneous

Igneous

Igneous rock is formed when lava cools and solidifies.

• 

  Basalt

• 

  Granite

• 

  Obsidian

• 

  Gabro

b. Sedimentary

Sedimentary

Sedimentary rock is formed when sediments carried by wind or water settle and turn to stone.

• 

  Chalk

• 

  Limestone

• 

  Sandstone

• 

  Shale

c. Metamorphic

Metamorphic

Metamorphic rock is formed when another type of rock is transformed by great heat and pressure.

• 

  Slate

• 

  Marble

• 

  Gneiss

• 

  Schist

4. What is meant by Mohs' scale of hardness? Name the minerals in order in Mohs' scale.

The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German mineralogist Friedrich Mohs and is one of several definitions of hardness in materials science.

Mohs based the scale on ten minerals that are all readily available. As the hardest known naturally occurring substance, diamond is at the top of the scale. The hardness of a material is measured against the 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 is 4.5.

The Mohs scale is a purely ordinal scale. For example, corundum (9) is twice as hard as topaz (8), but diamond (10) almost four times as hard as corundum. The table below shows comparison with absolute hardness measured by a sclerometer.

Hardness	Mineral	Absolute Hardness
1	Talc (Mg3Si4O10(OH)2)	1
2	Gypsum (CaSO4·2H2O)	2
3	Calcite (CaCO3)	9
4	Fluorite (CaF2)	21
5	Apatite (Ca5(PO4)3(OH-,Cl-,F-))	48
6	Orthoclase Feldspar (KAlSi3O8)	72
7	Quartz (SiO2)	100
8	Topaz (Al2SiO4(OH-,F-)2)	200
9	Corundum (Al2O3)	400
10	Diamond (C)	1500

On the Mohs scale, fingernail has hardness 2.5; copper penny, about 3.5; a knife blade, 5.5; window glass, 6.5; steel file, 6.5. Using these ordinary materials of known hardness can be a simple way to approximate the position of a mineral on the scale.

Some mnemonics traditionally taught to geology students to remember this table are "The Girls Can Flirt And Other Queer Things Can Do" or "To Get Candy From Aunt Fanny, Quit Teasing Cousin Danny". Another Mnemonic is "Two Gypsies Called Flo And Fred Queued To Cut Diamonds."

An alternative table is shown below which has been modified to incorporate additional substances that may fall in between two levels.

Source: American Federation of Mineralogical Societies: Mohs Scale of Mineral Hardness

Hardness	Substance or Mineral
1	Talc
2	Gypsum
2.5 to 3	pure Gold, Silver
3	Calcite, Copper penny
4	Fluorite
4 to 4.5	Platinum
4 to 5	Iron
5	Apatite
6	Orthoclase
6.5	Iron pyrite
6 to 7	Glass, Vitreous pure silica
7	Quartz
7 to 7.5	Garnet
7 to 8	Hardened steel
8	Topaz
9	Corundum
10	Diamond
11.1	Aggregated diamond nanorods

5. Define the following:

a. Cleavage

Adventist Youth Honors Answer Book/Nature/Rocks & Minerals/Cleavage

b. Specific gravity

Specific gravity is the ratio of the density of a material relative to the density of water. Density is the ratio of an object's mass to it's volume. For instance, we know that 1 cm^3 of water weighs 1 gram. Therefore, the density of water is:

[math]\displaystyle{ density_{water} = \frac{1 gram}{1 cm^3} = 1 }[/math]

The density of diamond is [math]\displaystyle{ 3.52 g/cm^3 }[/math] (meaning that a cubic centimeter of diamond would weigh 3.52 grams). This means that the specific gravity (G) of diamond is

[math]\displaystyle{ G = \frac{3.52g/cm^3}{1g/cm^3} = 3.52 }[/math]

Division by 1 is a lovely thing!

But what use is specific gravity? It helps us identify a mineral. We can measure a sample's specific gravity and compare it to the specific gravity of known specimens. Unfortunately, it is very difficult to determine the volume of an irregularly-shaped rock, but we will not let that stop us. All we have to do is weigh the sample, and then weigh it again while it is submerged in water.

[math]\displaystyle{ G = \frac{W}{W - F}\, }[/math]

Where

[math]\displaystyle{ G }[/math] is the relative density,

[math]\displaystyle{ W }[/math] is the weight of the sample (measured in the air)

[math]\displaystyle{ F }[/math] is the weight of the sample while the sample was submerged.

Going back to our diamond example, if the diamond weighed 4 grams in the air and 2.86 grams when submerged in water, we could calculate its specific gravity as

[math]\displaystyle{ G = \frac{W}{W - F} = \frac{4}{4 - 2.86} = \frac{4}{1.14} = 3.51 }[/math]

Which is very close to the 3.52 we had before.

Everything has some buoyancy, even things that sink in water. That is why the diamond weighs less when it's under water. If an object's specific gravity is less than 1, its under-water weight would be negative - meaning that instead of falling down, it would fall up - that is, it would float back to the surface.

7. Locate four Bible incidents in which a rock was significant.

Numbers 20:2-13

God commands Moses to strike a rock to provide the Israelites with water.

1 Samuel 17

David kills Goliath with a stone.

John 11:38-44

Jesus orders that the stone covering the tomb of Lazarus be removed.

Matthew 7:24-29

The parable of the wise and foolish builders.

Acts 6-7

The stoning of Stephen

8. List the foundation stones of the New Jerusalem and tell where you found the information.

Revelation 21:19,20 describes the foundation stones of the New Jerusalem.

1. Jasper	7. Chrysolite
2. Sapphire	8. Beryl
3. Chalcedony (Carbuncle?)	9. Topaz
4. Emerald	10. Chrysophase
5. Sardonyx	11. Jacinth (Turquoise?)
6. Sardus (Ruby?)	12. Amethyst (Chrystal?)

The wall has twelve foundation stones, and on these are written the names of the Twelve Apostles. Revelation lacks a list of the names of the Twelve Apostles, and does not describe which name is inscribed on which foundation stone, or if all of the names are inscribed on all of the foundation stones, so that aspect of the arrangement is open to speculation. One scholar hold that Judas Iscariot's name is absent from the foundations, replaced by that of another Apostle.

These foundation stones are adorned with twelve types of precious stones. In modern times, the precise identification of all these precious stones is not certain, as several of the ancient names may refer to several different types of stones, or may no longer refer to the same kinds of stones that they did at the time of Revelation's writing. Also, the layout of the precious stones is contested. All of the precious stones could adorn each foundation stone, either in layers or mixed together some other way, or just one unique type of stone could adorn each separate foundation stone.

References

Wikipedia Articles

• Mineral
• Mohs scale of hardness
• New Jerusalem