Hardness Scale

All naturally occuring rocks and minerals have inherent physical properties. The Hardness Scale developed by German geologist Friedrich Mohs in 1812 is a universal system for defining the hardness of natural materials.

10 : Diamond

Scratches all other minerals

9 : Corundum

Scratched by Diamond

8 : Topaz

Scratched by Corundum

7 : Quartz

Scratched by Topaz

6 : Feldspar

Scratched by steel file

5 : Apatite

Scratched by steel knife

4 : Fluorite

Easily scratched by steel knife

3 : Calcite

Scratched by copper coin

2 : Gypsum

Scratched by fingernail

1 : Talc

Easily scratched by fingernail

Butter Jade

Creamy, sandy. Brown or purple markings

Butter Jade is predominantly a creamy yellow colour, sometimes a subtle pale green, but with dark markings throughout. The striations found in the attractive yellow-green sedimentary rock are layers of fossilised algae, around 50 million years old. Although named so, it is not actually a true jade - this particular variation is called Nephrite, a cream or tan coloured Jade.

Mohs Hardness Rating : 6 - 7


Reds, purples, browns

Cobalt is a brittle, relatively rare hard metal, closely resembling iron and nickel in appearance.

This stone is a variety of Serpentine and is believed to be creatively and emotionally uplifting, 'heals all infections’ creating harmony with all that is: perfection. Cobalt is used in the treatment of cancer and cellular disorders.

Mohs Hardness Rating : 5 - 6

Opal Stone

Milky green. Brown markings

Opal stone is famous for it's milky light coloured greens and smooth texture. It is also known as opalite to the locals and is mined at Chiweshe, two hours north of Harare. This stone is one of the favourites of carvers - it is not as hard as Springstone and other serpentines, but still polishes to a high finish.

Opal stone occasionally has brown colours throughout the predominant green. The appearance can be smooth or mottled. Opal stone is also found in Australia and Mexico.

Mohs Hardness Rating : 5 - 5.5

Red Jasper

Reds, oranges, browns. Light or dark markings

Jasper, a form of chalcedony, is an opaque, impure variety of silica, occurring in virtually any colour, determined by the mineral content of the original sediments. Commonly red, green, yellow or brown in colour, and occasionally blue or purple. This mineral breaks with a smooth surface, and is used for ornamentation or as a gemstone.

The name Jasper, which has evolved through many different languages, means simply ‘spotted or speckled stone.’ It is believed to protect against sight defects and drought.

Mohs Hardness Rating : 7


Mottled greens, browns

Most serpentines are opaque or slightly translucent, and lustre may be vitreous, greasy or silky. It occurs in widespread locations worldwide, and there are many deposits throughout Zimbabwe, including the huge ‘Great Dyke’ which covers some 340miles. Hardness varies from very soft to hard. Most sculptors tend not to carve with softer serpentines however, but rather favour harder, more durable deposits.

Colours are usually greens, browns, greys and blacks, and are often mottled or veined. The common green colour and smooth, scaly appearance is believed to be the basis of the name, from the Latin serpentinus, meaning ‘serpent rock.’

Serpentine is a protective stone. It is considered especially protective against snakebite, parasite infections, poisons and venoms, and is an excellent stone for meditation.

Mohs Hardness Rating : 2.5 - 4


Dark grey or black. Brown or red markings

Springstone is one of the hardest stones used for sculpting in Zimbabwe. There are a few places where this stone is found, but Guruve, in the north, is where Springstone is mostly mined.

A beautiful dark stone, it polishes to a high shine because of its density. It will often feature a softer brown layer, which adds to the appeal. As with most other stones that are mined for the purpose of sculpture, this stone is mined by hand on communal lands.

Mohs Hardness Rating : 6 - 8


Rich green. Brown markings

Verdite has a unique emerald looking quality with brown and green striations and is known as 'green gold' because it is a semi-precious stone. It is unfortunately becoming rare and therefore increasingly valuable. It is a hard stone and only the more experienced sculptor will dare to sculpt it.

Mohs Hardness Rating : 8 - 9

White Opal

Creamy white. Rusty markings

White opal stone is a less common medium for Shona sculpture. The stone has a creamy, light beige, or ecru colour with darker tan mottling. Its appearance changes dramatically when polished, becoming a much deeper colour, and its descriptive name, no longer appropriate, is often misleading.

Mohs Hardness Rating : 5.5 - 6.5