Select all the properties of diamond.

Diamond has several unique properties:

1. Hardness: Diamond is the hardest known natural substance on Earth. It's rated 10 on the Mohs scale of mineral hardness.

2. High Refractive Index: Diamonds have a high refractive index, meaning they bend light to a high degree. This property gives diamonds their brilliant sparkle.

3. Thermal Conductivity: Diamonds have a high thermal conductivity, meaning they can conduct heat very efficiently.

4. Electrical Insulator: Despite being a good conductor of heat, diamond is a poor conductor of electricity.

5. High Density: Diamonds have a high density, meaning they are very heavy for their size.

6. Crystal Structure: Diamonds have a cubic crystal structure.

7. Transparency: Diamonds are transparent from the ultraviolet to infrared range.

8. Luster: Diamonds have an adamantine luster, meaning they have a brilliant shine.

9. Toughness: Although diamonds are very hard, they are not very tough. This means they can be chipped or cracked relatively easily.

10. Cleavage: Diamonds have perfect cleavage, meaning they can be split along certain planes.

These are some of the most notable properties of diamonds.