why do minerals have different physical properties?
The images above show three substances, that while they look very different, are actually all made from the exact same element. Diamonds, coal, and the graphite in your pencil are all made from only one element, Carbon. How can these three substances be made from the same thing if they are so different? To understand the source of these differences we have to look inside at the way that each substance's atoms are arranged.
The Internal Arrangement of Atoms
As you recall, one of the 5 requirements of all minerals is that they have an orderly arrangement of atoms. This is an important requirement because...
INTERNAL ARRANGEMENT OF ATOMS DETERMINES ALL OF A MINERAL'S PHYSICAL PROPERTIES
We will learn to observe and test the physical properties of minerals to help us identify them.
Physical Properties of Minerals
THE SHAPE OF A CRYSTAL IS DETERMINED BY THE INTERNAL ARRANGEMENT OF ATOMS.
Crystal shape is a physical property that can be identified simply by looking at the mineral. However, many minerals have the same crystal shape, so we will not use shape to help us identify minerals.
HARDNESS IS A MINERAL'S ABILITY TO RESIST SCRATCHING.
THE HARDNESS OF A MINERAL IS DETERMINED BY THE INTERNAL ARRANGEMENT OF ATOMS.
We test the hardness of a mineral by scratching it against other substances with known hardness, like fingernails, glass, steel, and copper pennies.
Based on what the mineral can and can't scratch we give it a hardness value using Moh's scale of harness.
BREAKAGE DESCRIBES THE WAY A MINERAL BREAKS.
THERE ARE TWO POSSIBLE TYPES OF BREAKAGE THAT A MINERAL CAN SHOW:
A MINERAL THAT SHOWS CLEAVAGE WILL BREAK ALONG FLAT SURFACES, AND HAVE SHARP, PRECISE CORNERS. Because of this minerals that show cleavage are often really geometric and cool looking.
A MINERAL THAT SHOWS FRACTURE WILL BREAK APART LIKE A RANDOM LUMP. They don't have smooth faces, or precise corners, but look irregular and lumpy.
THE TYPE OF BREAKAGE SHOWN BY A MINERAL IS DETERMINED BY THE INTERNAL ARRANGEMENT OF ATOMS
LUSTER DESCRIBES HOW A MINERAL REFLECTS LIGHT. Again, there are just two types of luster:
Metallic minerals look like they are made from metal.
Non-metallic minerals DO NOT look like they are made from metal.
THE TYPE OF LUSTER SHOWN BY A MINERAL IS DETERMINED BY THE INTERNAL ARRANGEMENT OF ATOMS
STREAK IS THE COLORFUL TRAIL A MINERAL LEAVES WHEN SCRATCHED AGAINST A CERAMIC TILE.
THE COLOR OF THE STREAK IS DIFFERENT FOR DIFFERENT MINERALS, AND NOT ALL MINERALS HAVE ANY STREAK.
A mineral's color depends on its INTERNAL ARRANGEMENT OF ATOMS. Because many minerals are the same color we will never identify a mineral based solely on its color.
Some minerals have unique properties that can be used to identify them. Because these properties are unique and rare, these properties are used less often in identification.
Some minerals like magnetite are magnetic.
Some minerals like Halite have a an identifiable taste. (We will never put any minerals or any other lab supplies near our mouths)
Reaction to Acid
Some minerals like Calcite will bubble and fizz when exposed to weak acids.