Mineral Identification Lab Purpose: In order to study the Earth we 1 st need to

ID: 296540 • Letter: M

Question

Mineral Identification Lab

Purpose: In order to study the Earth we 1st need to understand minerals, they are the building blocks of rocks. Mineral identification is necessary to identify rocks and can be used to understand both the landscape and the geologic history of the area. For example identifying pyrite in a rock tells the geologist that volcanoes were once present, and that there is a potential of finding gold or silver ore along with the pyrite.

In order to identify the mineral we will use a dichotomous key. A dichotomous key is a device that can be used to easily identify an unknown organism or mineral. The word dichotomous comes from two Greek words that together mean, "divided in two parts". A dichotomous key consists of a series of two part statements that describe characteristic of organisms. At each step of a dichotomous key the user is presented with two choices. As the user makes a choice about a particular characteristic of an organism they are led to a new branch of the key. Eventually the user will be led to the name of the organism or mineral that they are trying to identify.

Materials: mineral samples; hematite, sulfur, mica, calcite, magnetite, graphite, pyrite, quartz, 1M HCl, streak plate, glass plate

Dichotomous Key for Minerals

In the blank next to the number in the step of the dichotomous key write in the property tested such as hardness, luster, chemical properties. Test each mineral starting at #1, and follow the direction given for each number.

1) ________________________________

a) The mineral scratches glass go to #2

b) The mineral does not scratch glass go to #3

2) ________________________________

a) The mineral has metallic luster. The mineral is pyrite.

b) The mineral has a nonmetallic luster. The mineral is quartz.

3) ________________________________

a) It has a metallic luster. Go to #4

b) It has a nonmetallic luster. Go to #5

4) ________________________________

a) The mineral has a greasy feel. The mineral is graphite.

b) The mineral is magnetic. The mineral is magnetite.

5) ________________________________

a) The mineral 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. Go to #6.

b) It does not break along a plane which is considered fracture. Go to #7

6) _________________________________

a) The mineral bubbles when acid is added to it. The mineral is calcite.

b) it does not bubble in acid. The mineral is biotite mica.

7) _________________________________

a) The mineral leaves yellow powder on a ceramic plate. The mineral is sulfur.

b) The mineral leaves a re-brown streak. The mineral is hematite.

List the names of the minerals using the dichotomous key results.

1) ___________________________

2) ___________________________

3) ___________________________

4) ___________________________

5) ___________________________

6) ___________________________

7) ___________________________

8) ___________________________

Post Lab Questions:

1) Why is mineral identification important?

2) A mineral must occur __________ in the Earth’s crust. It cannot be manufactured or manmade.

3) Most minerals are _________ rather than organic. Organic materials are formed from ___________ things.

4) A mineral is usually always a __________________, thy are rarely liquids or gases.

5) A mineral has a definite chemical ____________________. They may be made of a single element or compound.

6) On Moh’s scale of hardness , ordinary window glass would have a hardness of _____

7) Which of the minerals that you identified are silicates?

8. What are the three most common elements on the Earth’s crust?

9. Why is color not a very reliable property to identify minerals?

10. What gas produces the bubbles when hydrochloric acid is added to some carbonate minerals?

Explanation / Answer

Sample 1:

1. b.) The mineral does not scratch glass.

3. b.) It has a non metallic lustre.

5. b.) It does not break along a plane which is considered fracture.

7. b.) The mineral leaves a re-brown streak. The mineral is hematite.

Sample 2 :