6. GYPSUM (CaSO_{4 @}H₂O) has a tabular crystalline structure and breaks in thick sheets. There are several forms of gypsum that have different uses. Alabaster is a fine grained variety of gypsum used by sculptors because it is soft and easy to carve. Gypsum is a common mineral found in sedimentary rocks. It is a calcium sulfate whose use is mainly in the production of plaster of Paris which is used in wall boards and other building materials. Gypsum is also used as a fertilizer and used in making concrete.   
     
   1. Is gypsum harder or softer than quartz?

2. How can you tell?

3. Describe the shape. Do you think it was broken or formed as a crystal? Why?

4. If you were naked on an island, and you found a mineral that you suspected was gypsum. How could you tell if it really was gypsum? 

7. PYRITE is usually found in crystals that are either cubic or octahedral. The chemical formula of pyrite is FeS_2. People commonly mistake pyrite for gold, hence its nickname "fool's gold." However, pyrite is a brassy color, while gold is yellow. The name pyrite is from the Greek word meaning fire, because it gives off sparks when struck with steel. Pyrite is used mainly to obtain sulfur for sulfuric acid.  
     

   1. What other mineral does pyrite resemble?

2. Describe pyrite's crystal form?

3. Use a streak plate (unglazed side) and determine the color of pyrite's streak.

4. Describe pyrite's luster.

5. What is the common name for pyrite?

8. HEMATITE is an iron oxide mineral with the formula Fe₂O₃. It occurs in different forms including gray-silvery metallic hematite and dull red earthy-looking hematite. Hematite can easily be identified by its brown red streak. Hematite is an important ore of iron, and is also used in making colors, such as red ocher and as a polishing powder.   
     
   1. Describe the two types of hematite. Why do you think that they are different?

2. Describe the color when hematite is "streaked" on a porcelain plate.

3. Describe the luster and color of your specimens of hematite.

4. Why do you think hematite is called "hematite?" (Clue hema = blood)