From Talc to Diamond: Moh's Scale of Hardness

		
The resistance of minerals to being scratched or abraded is
		known as the mineral's hardness. This hardness has been compared and
		tested as far back as 300 B.C. by the Greek philosopher Theophrastus
		and in 33 A.D. by the Roman author and philosopher Pliny the Elder.
		Both knew that the hardness of minerals could be determined by
		scratching one mineral against another. In 1812, a German mineralogist
		went a step further and created a hardness scale to use when testing
		mineral hardness. This scale is known as the Mohs Hardness Test, and
		it was designed by, and named after, Friedrich Mohs. Like Pliny the
		Elder and Theophrastus, Mohs knew that when rubbed together, the
		hardest of two minerals would leave a scratch on the other. He
		numbered his scale from one to 10 going from the softest to the
		hardest mineral. Each number on the scale is represented by a mineral
		and its hardness value. The minerals listed are meant to be used as a
		standard means to test and determine the hardness of other minerals.
		Although the scale was designed to measure the hardness of minerals,
		it is not meant to measure the exact degree of hardness. That is
		because the actual hardness of a mineral is based on factors such as
		the amount of crystallinity and its purity. In addition, it is also
		not meant to be a test of brittleness, which differs from hardness. In
		some cases, a mineral may be harder than others, like a diamond for
		example, but it may be extremely brittle as well. The following is the
		Mohs scale in order of softest to hardest mineral:

		
    
			
  • 1. Talc: Talc is rated as the softest of the minerals
			in general. Although talc is popularly recognized as talcum powder,
			it may also be used for a variety of other products, such as
			cosmetics.
    • 
			
  • 2. Gypsum: This is also a soft mineral. It is
			composed of sulfate dihydrate. Its uses include wallboard, Plaster of
			Paris, cement, and fertilizer.
    • 
			
  • 3. Calcite: Calcite is a mineral that is commonly
			used in animal feeding as a dietary supplement and can be found in
			antacids for humans. It is in marble and limestone rocks and can be
			found hanging from the walls of caves. It is a carbonate and a highly
			distributed mineral that may appear as different forms of crystals.
    • 
			
  • 4. Fluorite: Fluorite is a mineral that can be found
			in various places worldwide. It has many industrial uses and is used
			frequently in common items such as enamel, lenses for cameras and
			telescopes, and in steel manufacturing. In appearance it can be found
			in various colors.
    • 
			
  • 5. Apatite: Apatite is commonly used in fertilizer
			because it is a source of phosphorous. The term apatite refers to a
			group of phosphate minerals. These are fluoraptite, hydroxylapatite
			and chlorapatite. It can be found in colors such as violet, green,
			yellow, or brown. It may also appear colorless.
    • 
			
  • 6. Orthoclase: Orthoclase is frequently used as an
			ingredient in porcelain and porcelain items, such as dolls. It is
			also widely used in glass and ceramics. Orthoclase also goes by the
			name of Feldspar.
    • 
			
  • 7. Quartz: This is a highly recognizable mineral that
			is used for numerous purposes, including as a gemstone for jewelry.
			Historically it was used to create arrowheads due to its hardness. It
			is highly heat-resistant and is used in bricks for this reason. Other
			uses for quartz include the making of fiberglass and glass. Different
			types of quartz include citrine, amethyst, rose quartz, and smoky
			quartz.
    • 
			
  • 8. Topaz: This mineral is a very common gemstone that
			is frequently used in jewelry. It can be found in a host of different
			colors such as brown, blue, yellow, pink, and orange. Much of its
			popularity stems from its clarity and hardness.
    • 
			
  • 9. Corundum: Corundum is the second hardest mineral
			behind the diamond. Both rubies and sapphires are types of popular
			corundum used in jewelry. Both rubies and sapphires are precious
			stones. Corundum also has its industrial uses and is used in
			sandpaper and cutting tools.
    • 
			
  • 10. Diamond: The hardest mineral is also one of the
			most beautiful and sought after in the world. While most people will
			associate diamonds with jewelry such as necklaces, rings, or
			earrings, their hardness makes them a valuable tool as well. Diamond
			particles can be used in tools made for cutting, grinding or
			drilling. When in powder form, it has also been added to polishes.
    • 
		

		
The minerals that are used may not always be readily available
		for testing purposes. For this reason, there are alternative objects
		that can be used in the place of the ten items in the Mohs Hardness
		Scale. These items also have a specific hardness level or number that
		is associated with them for testing. They are items that people
		typically have in their possession, which makes them ideal for use as
		a demonstration or as a project for children. Objects that are
		commonly used for testing include fingernails, a copper penny, a knife
		made of steel or a glass plate, and a steel file. The hardness of
		these items ranges from 2.5 for a fingernail and up to 6.5 for a file
		that is made of steel. Between the least and hardest objects on the
		alternate list is a penny, which has a standard hardness of 3. A glass
		plate has a hardness value of 5.5. When using these objects, the
		hardness of the mineral that is being tested can be determined up to
		the scales nearest half number.

		
Performing the hardness test is relatively simple, but there
		are certain rules that should be remembered. The first is that if two
		objects are of the same hardness, they may be scratched but with
		difficulty. The second principle to remember is that the mineral or
		object that creates the scratch is always harder than the object that
		receives the scratch. Keeping these in mind, the person performing the
		test should start with a mineral or object that is at the softest end
		of the scale. This may be one's fingernail or talc depending on which
		test objects are being used. Beginning with the softest of the objects
		allows for the simplest process of elimination. If the object does not
		scratch, then the next hardest object is used until a scratch is made.
		When attempting to scratch the surface, the tester will ideally want
		to save the surface and quality of the mineral in question. To do
		this, the mineral being tested should be used to scratch the surface
		of the penny, glass plate, or other test objects such as the minerals
		listed on the Mohs scale.