1. Color: The visual appearance of a substance, such as blue, red, or green.

2. Density: The ratio of mass to volume, which indicates how tightly packed the molecules of a substance are.

3. Melting Point: The temperature at which a solid changes into a liquid.

4. Boiling Point: The temperature at which a liquid changes into a gas.

5. Conductivity: The ability of a substance to conduct heat or electricity.

6. Hardness: The resistance of a solid to scratching or indentation.

These properties are all observable and can be measured without changing the chemical composition of the substance.