Tourmaline

Tourmaline

Hardness
7 to 7.5
Refractive index
1.620 to 1.650 birefringence from 0.014 to 0.021
Specific gravity
3.00 to 3.10

Nomenclature

Shape

Indicative weight

– carats

Dimensions (mm)Weight (ct)

A calibrated series, to scale

All shapes side by side
Round
Dimensions (mm)Weight (ct)
2.00.04
2.50.07
3.00.12
3.50.16
4.00.29
4.50.35
5.00.52
5.50.66
6.00.86
7.01.65
Oval
Dimensions (mm)Weight (ct)
4 × 30.15
5 × 30.24
6 × 40.48
7 × 50.82
8 × 61.22
9 × 71.85
10 × 82.59
11 × 93.63
12 × 104.52
14 × 105.43
Marquise
Dimensions (mm)Weight (ct)
4 × 20.09
5 × 2.50.18
6 × 30.27
8 × 40.60
10 × 51.15
12 × 61.74
15 × 73.33
16 × 83.97
18 × 95.93
20 × 108.62
Heart
Dimensions (mm)Weight (ct)
3.00.09
4.00.21
4.50.38
5.00.46
5.50.65
6.00.77
7.01.24
8.01.75
9.02.41
10.03.59
Octagon
Dimensions (mm)Weight (ct)
4 × 30.21
5 × 30.28
6 × 40.35
7 × 51.18
8 × 61.73
9 × 72.51
10 × 83.84
11 × 95.24
12 × 106.48
14 × 106.66
Pear
Dimensions (mm)Weight (ct)
5 × 30.20
6 × 40.40
7 × 50.69
8 × 50.88
9 × 61.41
10 × 71.92
12 × 83.08
14 × 94.33
15 × 105.65
16 × 128.32
Square
Dimensions (mm)Weight (ct)
2.00.05
2.50.08
3.00.16
3.50.22
4.00.34
4.50.53
5.00.62
5.50.75
6.01.12
7.01.82

Sources

The main deposits are in Brazil, Nigeria and Mozambique.

Common treatments

Heat-treatment is very common for tourmalines.

They might also be filled with oil, wax or resin if they have cracks, or with epoxy resin if they have large fractures.

Care and cleaning

Tourmaline attracts dust and therefore needs a regular cleaning.

– Avoid ultrasound and steam jets

– Avoid heat and thermal shocks as it may change the gem’s colour or enlarge a pre-existing fracture

– Keep treated tourmalines away from acidic substances as well.