ISLAND SOAPSTONE

Some Soapstone History

People have quarried soapstone for thousands of years. Native Americans in eastern North America used the soft rock to make bowls, cooking slabs, smoking pipes and ornaments as early as the Late Archaic Period (3000 to 5000 years ago). [1] Native Americans on the west coast traveled in canoes from the mainland to San Clemente Island (60 miles offshore!) to obtain soapstone for cooking bowls and effigy carving as early as 8000 years ago. [2]

The people of Scandinavia began using soapstone during the Stone Age and it helped them enter the Bronze Age when they discovered that it could be easily carved into molds for casting metal objects such as knife blades and spearheads. They were among the first to discover the ability of soapstone to absorb heat and radiate it slowly. That discovery inspired them to make soapstone cooking pots, bowls, cooking slabs and hearth liners. [3]

Throughout the world, in locations where the soapstone is exposed at the surface, it was one of the first rocks to be quarried. Soapstone’s special properties continue to make it the “material of choice” for a wide variety of uses.

What is Soapstone?

Soapstone is a metamorphic rock that is composed primarily of talc, with varying amounts of chlorite, micas, amphiboles, carbonates and other minerals. [4] Because it is composed primarily of talc it is usually very soft (for a rock, that is!) Soapstone is typically gray, bluish, green or brown in color, often variegated. Its name is derived from its “soapy” feel and softness.

The name “soapstone” is often used in other ways. Miners and drillers use the name for any soft rock that is soapy or slippery to the touch. In the craft marketplace, sculptures and ornamental objects made from soft rocks such as alabaster or serpentine are often said to be made from “soapstone.” Be careful when purchasing if the type of rock used in making the object is important to you.

Many people use the name “steatite” interchangeably with “soapstone.” However, some people reserve the name “steatite” for a fine-grained unfoliated soapstone that is nearly 100% talc and highly suited for carving.

How Does Soapstone Form?

Soapstone most often forms at convergent plate boundaries where broad areas of Earth’s crust are subjected to heat and directed pressure. Peridotites, dunites and serpentinites in this environment can be metamorphosed into soapstone. On a smaller scale soapstone can form where siliceous dolostones are altered by hot, chemically-active fluids in a process known as metasomatism.

Physical Properties of Soapstone

• Soapstone is composed primarily of talc and shares many physical properties with that mineral. These attributes make soapstone valuable for many different uses. Some of these properties include:
• nonporous
• nonabsorbent
• low electrical conductivity
• heat resistant
• high specific heat capacity
• resistant to acids and alkalis

Soapstone is a rock and its mineral composition can vary. Its composition depends upon the parent rock material and the temperature/pressure conditions of its metamorphic environment. As a result, the physical properties of the soapstone can vary from quarry to quarry and even within a single rock unit.

The level of metamorphism sometimes determines its grain size. Soapstone with a fine grain size works best for highly detailed carvings. The presence of minerals other than talc and the level of metamorphism can influence its hardness. Some of the harder varieties of soapstone are preferred for countertops because they are more durable than a pure talc soapstone.

How is Soapstone Used?

The special properties of soapstone make it suitable, or the material of choice, for a wide variety of uses. A number of examples of soapstone use are:

• Countertops in kitchens and laboratories
• Sinks
• Cooking pots, cooking slabs, boiling stones
• Bowls and plates
• Cemetery markers
• Electrical panels
• Ornamental carvings and sculptures
• Fireplace liners and hearths
• Woodstoves
• Wall tiles and floor tiles
• Facing stone
• Bed warmers
• Marking pencils
• Molds for metal casting
• Cold stones

Soapstone Kitchen and Laboratory Countertops

Soapstone is often used as an alternative natural stone countertop instead of granite or marble. In laboratories it is unaffected by acids and alkalis. In kitchens it is not stained or altered by tomatoes, wine, vinegar, grape juice or other common food items. Soapstone is unaffected by heat. Hot pots can be placed directly on it without fear of melting, burning or other damage.

Soapstone is a soft rock and it is easily scratched in countertop use. However, a gentle sanding or treatment with mineral oil will easily remove or render shallow scratches invisible. Soapstone is not suitable for use as a workbench top where it will receive rough treatment or where sharp or abrasive objects will be placed upon it.

Soapstone Tiles and Wall Panels

Soapstone tiles and panels are an excellent choice where heat and moisture are present. Soapstone is dense, without pores, does not stain and repels water. Those properties make soapstone tiles and wall panels a good choice for showers, tub surrounds and backsplashes.

Soapstone is heat resistant and does not burn. That makes it an excellent wall covering behind wood burning stoves and ovens. Fireplaces are also lined with soapstone to create a hearth that quickly absorbs heat and radiates it long after the fire is out. This property of soapstone was recognized in Europe over 1000 years ago and many early hearths there were lined with soapstone.

Soapstone Woodstoves

Soapstone does not burn or melt at wood burning temperatures and it has the ability to absorb, hold and radiate heat. These properties make it an excellent material for making wood-burning stoves. The stove becomes hot and radiates that heat into the room. It also holds heat, keeping the coals hot and often allowing the owner to add more wood without the need for kindling.

Soapstone Cooking Pots

Soapstone cooking pots absorb heat readily from the stove and radiate it into the soup or stew. Because their walls are thick they take a little longer to heat than a thin metal pot. However, they heat their contents evenly and retain their heat when removed from the stove - the contents of the pot keep cooking until the pot itself begins to cool. Soapstone pots are highly prized by people who have learnt how to use them.

Stone Age people made the first cooking pots from soapstone without the aid of metal tools. The soft rock could be worked with sharp stones, antlers or bone. Skilled craftsmen carved the pots directly from the outcrop. Small soapstone pots were highly prized and traded widely. Large soapstone pots were very heavy and difficult to move. Archaeologists believe that large soapstone pots were used at sites where the residents had intentions of living for a long time.

In short: Soapstone has been a household mainstay since early human history - its practicality only enhanced by its versatility and timeless beauty.

Footnotes:

[1] Origin of Soapstone within the Wissahickon Formation: Analyses of Native American Quarries along the Lower Patuxent River, Maryland; Rachel Burks, Steven Lev and Wayne Clark, Geological Society of America, Abstracts with Programs, Vol. 38, No. 7, p. 234, October, 2006.

[2] California's Ancient Maritime Heritage, John W. Foster, California Department of Parks and Recreation, website article accessed, June, 2012.

[3] Soapstone Production through Norwegian History: Geology, Properties, Quarrying and Use; Per Storemyr and Tom Heldal; in: Asmosia 5: Interdisciplinary Studies on Ancient Stone; ppg. 359-369; J.J. Herrmann, N. Herz and R. Newman, editors; Archetype Publications Ltd, 2002.

[4] Talc: The Softest Mineral: Website article by geology.com staff, April, 2012.

Author: Hobart M. King, PhD

Source: Geology.com Geoscience News and Information