1. Streak: The color of a mineral's powder, which is often different from its external color. This is obtained by rubbing the mineral against an unglazed porcelain tile. It's a very consistent property, even if the mineral's color varies due to impurities.
2. Hardness: A mineral's resistance to scratching. This is often measured using Mohs Hardness Scale, where a mineral can scratch any mineral softer than itself. Knowing a mineral's hardness can be a key identifier.
3. Cleavage: The tendency of a mineral to break along specific planes of weakness. This creates smooth, flat surfaces. The type and quality of cleavage (perfect, good, poor) are useful for identification.
4. Fracture: How a mineral breaks when it doesn't have cleavage. Types include conchoidal (shell-like), uneven, hackly (jagged), or splintery.
5. Luster: The way light reflects off the surface of a mineral. Common types include metallic, glassy, pearly, resinous, and dull.
Bonus Property:
* Specific Gravity: The ratio of a mineral's density to the density of water. While more involved to measure, it can be very helpful in distinguishing between minerals that look alike.
Remember, it's usually best to consider multiple properties when identifying minerals. Don't rely on just one!