Hardness
* Definition: Hardness describes a mineral's resistance to scratching. It's a measure of how strongly the atoms in the mineral's structure are bonded together.
* Testing: Hardness is determined using the Mohs Hardness Scale, which ranks minerals from 1 (softest - talc) to 10 (hardest - diamond). You test a mineral's hardness by seeing if it can scratch, or be scratched by, a known mineral on the scale.
* Significance: Hardness helps identify minerals and understand their properties. For example, a diamond's hardness is why it's used in jewelry and tools.
Streak
* Definition: Streak refers to the color of a mineral's powder when it is rubbed against a streak plate (unglazed porcelain).
* Testing: You simply rub the mineral across the streak plate to see the color of the powder it leaves behind.
* Significance: Streak is often more reliable than a mineral's external color for identification because the streak color is less affected by impurities or weathering.
Key Differences
* Property: Hardness measures resistance to scratching, while streak measures the color of the powdered mineral.
* Testing: Hardness is tested by scratching, while streak is tested by rubbing.
* Reliability: Streak is often more reliable for identification than color because it's less susceptible to external factors.
Example
Consider Pyrite, often called "fool's gold." It has a metallic gold color, but its streak is black. This difference in color helps distinguish it from real gold, which has a golden streak.
