Mineral Properties
There are 8 ways to check mineral properties:
1. Hardness
2. Cleavage
3. Fracture
4. Streak
5. Luster
6. Color
7. Magnetism
8. Hydrochloric Acid
1. Hardness
2. Cleavage
3. Fracture
4. Streak
5. Luster
6. Color
7. Magnetism
8. Hydrochloric Acid
Hardness
Hardness is found by scratching a mineral with different objects. The picture at the left is Moh's Scale of Hardness. It ranges from 1 to 10. 1 being the softest or the easiest to scratch and 10 being the hardest. In the lab we will be using common objects like glass, nails, pennies, and fingernails to scratch our minerals to find out the hardness. The mineral that is scratched is softer than the thing doing the scratching.
For example, if I have a mineral that I can scratch with my fingernail it is softer than a 2.5. If I have a mineral that scratches my fingernail and gets scratched by a penny, it's hardness is between 2.5 and 3.5.
For example, if I have a mineral that I can scratch with my fingernail it is softer than a 2.5. If I have a mineral that scratches my fingernail and gets scratched by a penny, it's hardness is between 2.5 and 3.5.
Cleavage
The word cleave means to break in two. So cleavage means a break with a flat, smooth surface. This break is natural. It happens because the atoms or molecules in the mineral are lined up to break apart in those flat surfaces.
There are 4 types of cleavage. They are commonly known as "one directional", "two directional", three directional", and "four directional" cleavage. But we'll categorize them by what they look like.
One directional looks like sheets or strings that come off a mineral naturally.
Two directional looks blocky. It will have 2 flat, smooth sides coming to a point. It's almost a cube but not quite.
Three directional is cubic. It has 3 flat, smooth sides coming to a point.
Four directional looks like a pyramid. The picture at the left is four directional. Its a little more complex however because it has 2 pyramids connected at the base. So it looks almost like a diamond shape.
There are 4 types of cleavage. They are commonly known as "one directional", "two directional", three directional", and "four directional" cleavage. But we'll categorize them by what they look like.
One directional looks like sheets or strings that come off a mineral naturally.
Two directional looks blocky. It will have 2 flat, smooth sides coming to a point. It's almost a cube but not quite.
Three directional is cubic. It has 3 flat, smooth sides coming to a point.
Four directional looks like a pyramid. The picture at the left is four directional. Its a little more complex however because it has 2 pyramids connected at the base. So it looks almost like a diamond shape.
Fracture
Fracture is the way a mineral breaks other than cleavage. So if it breaks along a smooth surface that is NOT flat, that would be a fracture. The obsidian at the left is an example of that. It can also break and leave a bumpy surface. That would be a fracture too.
Streak
Streak is defined as the color of the mineral in powder form. This is a great indicator of a mineral because the streak is always the same. Even if the mineral is a different color than usual due to impurities, the streak will still be the same.
Streak is sometimes surprising. A black mineral can streak red or even white.
Streak is sometimes surprising. A black mineral can streak red or even white.
Luster
Luster is defined as the quality of reflected light. Or the "shinyness" of a mineral. There are 3 catagories:
1. Metallic. This means the mineral looks and glints in the light like a metal. So it could look like gold, silver, bronze, brass, or any other metal. The mineral at the right has a metallic luster.
2. Non-metallic. This means the mineral does NOT look like a metal. Sometimes it will still glint in the light but not like a metal does.
3. Vitreous. This means the mineral looks "glassy". It reflects light like glass does. It may be colored glass, but still glass. Technically, vitreous is non-metallic but knowing this term will help you identify minerals easier.
1. Metallic. This means the mineral looks and glints in the light like a metal. So it could look like gold, silver, bronze, brass, or any other metal. The mineral at the right has a metallic luster.
2. Non-metallic. This means the mineral does NOT look like a metal. Sometimes it will still glint in the light but not like a metal does.
3. Vitreous. This means the mineral looks "glassy". It reflects light like glass does. It may be colored glass, but still glass. Technically, vitreous is non-metallic but knowing this term will help you identify minerals easier.
Color
Color is not a good indicator of a mineral. The slightest impurity in a substance can change it's color. To the left are 5 samples of calcite. They are different colors due to impurities. (The streak of all of those will still be the same though!)
There are SOME minerals that are always the same color like sulfur, malachite, and azurite. But it never hurts to do another test on the mineral before deciding what it is.
Moral of the story: Don't trust the color.
There are SOME minerals that are always the same color like sulfur, malachite, and azurite. But it never hurts to do another test on the mineral before deciding what it is.
Moral of the story: Don't trust the color.
Magnetism
Magnets can help you find minerals like magnetite. Magnetite is not a magnet itself but a magnet will stick to it.
Lodestone is a mineral that IS a magnet. Paperclips will stick to it.
Lodestone is a mineral that IS a magnet. Paperclips will stick to it.
Reaction to Hydrochloric Acid
There are several minerals that are clear and cubic and look very similar. A couple drops of hydrochloric acid will tell you if the mineral has calcium carbonate in it. If it does, it's likely calcite or a type of limestone. If it bubbles and fizzes, then it has calcium carbonate.