Serpentine is the state rock of California
Serpentine is a group of minerals known for their smooth, waxy texture and green colors.
It is often used in carvings, decorative items, and even as a building material. Some varieties are so jade-like that they are mistaken for jade.
Serpentine vs Serpentinite
A rock made mostly of serpentine minerals is called serpentinite. While these two terms are often used interchangeably, they are not the same. Serpentine refers to the minerals, while serpentinite refers to the rock.
Why is it Called Serpentine?
The term "serpentine" comes from the Latin word serpens, meaning "snake."
Early geologists and collectors noticed the mineral's unique green color, often mottled or patterned in a way that looked like snakeskin.
Some types of serpentine even have a scaly or fibrous texture, enhancing their snake-like appearance.
Serpentine Colors and Varieties
Serpentine comes in many colors, influenced by the minerals and impurities it contains. Common varieties include:
- Green serpentine: A classic light to dark green shade, often with a smooth, waxy finish.
- Yellow-green serpentine: A pale yellowish-green hue, sometimes translucent.
- Gray-green serpentine: A muted, earthy green often mixed with darker tones.
- Brownish-black serpentine: Green mixed with brown or black inclusions, giving it a mottled look.
Some serpentine specimens contain fibrous asbestos and may display a shimmering effect called chatoyancy, similar to "cat's eye" gemstones.
Serpentine Formation
Serpentine minerals form through a process called serpentinization. It occurs when heat and water alter ultramafic rocks rich in magnesium and iron, like peridotite and dunite.
Both of these rocks are often found deep below the Earth's crust or in oceanic plates. When water enters through cracks or during tectonic collisions, it interacts with the minerals, causing a transformation.
The process is unique because it doesn't rely solely on high heat and pressure, like most metamorphic changes, but rather on the interaction of water with the original minerals. This reaction creates serpentine minerals such as lizardite, antigorite, and chrysotile, along with other byproducts like magnetite and hydrogen gas. The chemical reaction is also exothermic—it releases heat, which can further drive the process.
Serpentinization often happens in subduction zones, where oceanic plates are pushed under continental plates, or in areas where pieces of the Earth's mantle have been exposed at the surface.
As a result, huge serpentine minerals and serpentinite rock deposits can form, often in mountainous regions or along ancient oceanic crust.
Guide to Serpentine Identification
Examine the Appearance
You can recognize serpentine by its distinctive color and texture. It is often dark green to black, with a mottled or snakeskin-like pattern. The surface often appears smooth, and some specimens show veins of lighter green or white serpentine minerals crisscrossing the rock.
Common Colors Include:
- Dark green: The most typical shade, often with a waxy or shiny surface.
- Gray-green: A muted, earthy green often mixed with darker tones.
- Black: Sometimes mixed with green or brown streaks, giving it a marbled look.
- Yellow-green: A lighter, pale green color, though less common.
Serpentine often has a compact structure, with grains or bands visible in some specimens.
Look for Special Properties
Serpentine has several unique features that make it easy to identify:
- Smooth and waxy: The surface feels greasy or silky to the touch. It also reflects light in a way that looks slightly greasy or dull.
- Mottled pattern: The snakeskin-like appearance on some rocks is a key giveaway.
- Veins of lighter minerals: Crisscrossing white or pale green lines are often visible.
These traits make serpentine stand out from other dark green rocks.
Some varieties of serpentine can also exhibit chatoyancy, a shimmering effect similar to a cat's eye, which can be seen when polished.
Test the Hardness
If you're unsure whether you've found serpentine, try scratching it:
- Serpentine is soft to moderately hard (3–5 on the Mohs scale).
- It can often be scratched with a knife or harder minerals like quartz.
Where to Find Serpentine?
You can find this mineral in many locations worldwide, often in regions where ancient oceanic crust has been pushed onto land. Here are some of the best-known areas to find serpentine:
North America
California, USA: Serpentine is California's state rock and is abundant in road cuts, quarries, and mountainous areas.
Oregon, USA: Common in Josephine County and near Myrtle Creek, where large serpentine formations are visible.
Vermont, USA: Found in the Appalachian Mountains, often alongside talc deposits.
North Carolina, USA: Known for high-quality serpentine specimens in the Blue Ridge Mountains.
Europe
Cornwall, England: Famous for green serpentine, particularly on the Lizard Peninsula.
Shetland Islands, Scotland: Known for dark green serpentine with a mottled appearance.
Liguria, Italy: Home to beautifully veined serpentine in the Apennine Mountains.
Pyrenees, France: Found in metamorphic zones along the mountain ranges.
Asia
Afghanistan: Known for green serpentine used in carvings and decorative items.
China: Produces raw serpentine and polished items for export.
Turkey: Common in regions with ultramafic rock formations.
Other Notable Locations
New Zealand: Found along mountain ranges and fault lines, particularly on the South Island.
Africa: Deposits are scattered across Morocco and South Africa.
South America: Serpentine is found in regions like the Andes Mountains, particularly in Peru.
Serpentine Processing Tips
Serpentine is relatively soft and fragile, requiring careful handling during extraction and preparation.
- Extraction: Use gentle tools to avoid damaging the rock. Serpentine's waxy surface can chip or crack under excessive pressure.
- Cleaning: Wash serpentine with warm water and a soft brush to remove dirt. Do not use harsh chemicals, as they may damage the surface.
- Polishing: Serpentine polishes beautifully, revealing its snakeskin-like patterns. Use a fine-grit polishing wheel and finish with a high-quality polish to enhance its luster.
Due to its softness, serpentine is not ideal for all jewelry, but it works well for carvings, tiles, and decorative pieces. Handle polished items carefully to prevent scratches or dulling.
Safety Note: Some Serpentine Contains Asbestos
One important thing to remember is that some types of serpentine, like chrysotile, contain asbestos fibers. These fibers can be harmful if inhaled.
If you're collecting or cutting serpentine, take precautions:
- Always wear a mask to prevent inhaling dust.
- Handle asbestos-rich specimens with care.
History and Uses of Serpentine
Serpentine has been valued for its unique look and versatility. Ancient people used it for carvings, amulets, and ornaments because it looked like jade.
Some cultures believed serpentine had protective powers and used it as a talisman to protect against evil.
During the Renaissance, serpentine became popular in Europe as a decorative material for architectural features and sculptures.
In the 18th and 19th centuries, when mixed with magnesite, it was used to craft intricate smoking pipes, known as meerschaum.
In architecture, serpentine, often referred to as "green marble," is used as a building material for countertops, tiles, and even sculptures.
Historically, serpentine has also been used to create heat-resistant items like cooking utensils and insulators.
