Hardness

(Moh’s scale)

Refractive Index

Density

(g/cm³)

Typical Particle Shape

Diameter (µm)

Calcite

2.9 - 3.0

1.66

2.71

Rosette, scalenohedral,

rhombohedral

0.8 - 2

Aragonite

3.5 - 4

1.68

2.95

Needle, rosette

1 - 3

TiO₂ (rutile)

6 - 7

2.7

4.23

Spherical/rounded

0.3 - 0.35

Kaolin

2

1.36

2.65

Platy, bookettes

2 - 5