There are many different types of dark brown stones that can be found in nature. The most common dark brown stones include granite, basalt, schist, and slate. The specific name of a dark brown stone depends on its mineral composition and texture. This article will provide an overview of some of the most common dark brown stones and their key identifying characteristics.
Granite
Granite is an igneous rock that forms when magma slowly cools below the surface of the Earth. It is primarily composed of quartz, feldspar, and mica minerals. Granite can form large mineral crystals visible to the naked eye, giving it a coarse texture. The most common color of granite is gray, but it also occurs naturally in shades of pink, black, brown, and white.
Dark brown granite gets its color from higher concentrations of mafic minerals like biotite, hornblende, and pyroxene. These minerals contain more iron and magnesium, giving the granite an overall darker hue. Locations where dark brown granite can be found include Brazil, Zimbabwe, China, and parts of Canada. The coarse texture and visible flecks of minerals help distinguish granite from other brown rocks.
Basalt
Basalt is an extrusive igneous rock, meaning it is formed by lava cooling rapidly on the surface of the Earth. It has a fine-grained texture and is composed primarily of the minerals plagioclase, pyroxene, and olivine. Basalt is dark in color due to the high amounts of iron and magnesium in its mineral composition.
Dark brown basalt occurs in many locations across the globe, including the western United States, Siberia, India, and Hawaii. Smooth, rounded surfaces on basalt help identify it, as it forms fluid lava flows before cooling. Basalt also frequently displays small cavities known as vesicles, caused by gas bubbles in lava. Distinctive column-shaped fracturing may also be visible. The dark brown color, fine texture, and surface features make basalt easy to distinguish.
Schist
Schist is a metamorphic rock, meaning it formed when an existing rock was subjected to high pressures and temperatures that altered its composition and texture. The minerals in schist, like mica and talc, tend to form parallel banding which allows the rock to split into sheets.
Schist can range in color but often appears medium to dark brown. The brown varieties contain iron-rich minerals like biotite mica and tend to form in iron-rich sedimentary rocks like shale. Locations where dark brown schists form include mountain ranges that have undergone metamorphism, like the Appalachians in the United States. In addition to parallel banding, schist may have a sparkly appearance from mica flakes. The layered texture helps identify it as a schist.
Slate
Slate is a fine-grained metamorphic rock that forms when shale is subjected to high pressures. During metamorphism, slate develops parallel alignments of minerals like mica, chlorite, and quartz. This gives slate a property called fissility that allows it to split into thin sheets.
Slate can form in various shades of grey, black, green, purple, and brown. Dark brown slate contains more iron-bearing minerals like biotite and hematite. It forms through metamorphism of iron-rich shale. Slate has been used as roofing material for centuries due to its durability and fissility. Locations where dark brown slate can be found include Wales, China, Belgium, and parts of the northeastern United States. The thin splitting layers make slate identifiable.
Identifying Dark Brown Stones
When trying to identify a specific dark brown stone, there are some key features to look for:
- Granite – Coarse grained, visible mineral grains, granular texture
- Basalt – Fine grained, smooth or dimpled surface, may have visible vesicles
- Schist – Medium to coarse grained, parallel mineral banding, layers or sheets, mica flakes visible
- Slate – Extremely fine grained, thin splitting sheets, smooth cleavage faces
The mineral composition and texture of a stone can help narrow down which specific rock type it is. Keep in mind that color alone is not enough to conclusively identify a dark brown stone. Overlapping mineral content in different rock types can produce similar dark brown hues. Additional structural and surface features provide the detail needed for accurate identification.
Uses of Dark Brown Stone
Dark brown stones like granite, basalt, schist, and slate have many applications because of their durability and aesthetics:
Construction Aggregate
Crushed stone aggregate made from dark brown rocks is commonly used in construction materials like concrete and asphalt. The hard, strong nature of rocks like basalt and granite make them ideal for mixing into cement or paving materials. Aggregate provides bulk strength and wear resistance.
Dimension Stone
Large blocks of dark brown stone are cut and finished for structural and decorative dimension stone. Granite, schist, and slate are popular choices for applications like building facades, countertops, floor tiles, and monuments because of their ability to take a polished finish. The swirls and patterns in the stone create one-of-a-kind designs.
Decorative Landscaping Stone
For decorative gardens, pathways, drainage, and landscaping, dark brown stone provides an attractive natural element. The shapes and textures of stone varieties like river rock slate and crushed granite lend organic appeal to designs. Dark brown hues blend with natural landscapes.
Roofing
Slate has been used to roof buildings for centuries. The thin, splitting layers make it suitable for forming durable and attractive roof shingles. Dark brown slate blends well with roofing materials while providing weather resistance. Durable granite and basalt are also occasionally used for roofing tiles.
| Stone Type | Common Uses |
|---|---|
| Granite | Construction aggregate, dimension stone, landscaping, occasionally roofing |
| Basalt | Construction aggregate, dimension stone, landscaping |
| Schist | Dimension stone, decorative aggregate, occasionally roofing |
| Slate | Roofing, dimension stone, landscaping, decorative aggregate |
Notable Dark Brown Stones
Some of the most famous and significant dark brown stones include:
Larvikite
– A dark brown igneous rock from the Larvik region of Norway
– Known for its beautiful blue iridescence and polished finish
– Used as a popular dimension stone for countertops and building facades
Labradorite
– A feldspar mineral found within dark gray to black igneous rocks
– Displays an optical phenomenon called labradorescence
– Polished labradorite exhibits a stunning play of iridescent blues, purples, and greens
Desert Brown
– A variety of dark brown granite quarried in Saudi Arabia
– Features distinctive contrasting patterns of brown, black, and cream minerals
– Popular as an exotic dimension stone in luxury architecture
Black Diamond Slate
– A very dark gray to brown-black slate from New York and Vermont
– Highly durable slate used for roofing shingles since the 19th century
– Has a smooth cleavage and takes on a slight luster when split
Geographic Sources
Some of the best known global sources for dark brown building and decorative stones include:
- Larvik, Norway – Larvikite dimension stone
- Labrador, Canada – Labradorite crystals
- Saudi Arabia – Desert brown granite
- India – Brown basalt, schists
- Brazil – Dark brown granite
- Vermont and New York, USA – Black diamond slate
- Wales – Brown slate
- Belgium – Blue/brown ledenian stone
The local geology affects the variety of dark brown stones found in any given region. Iron-rich sedimentary deposits tend to metamorphose into brown schists and slates. Areas with iron-rich volcanic flows produce dark basalts and granites. The best sources for high quality decorative brown stone are found near ancient mountain belts and ancient volcanic regions.
Price Range
Dark brown dimensional building stone can range dramatically in price due to factors like rarity, location of origin, size of slabs or blocks, and processing required. Some typical price ranges include:
- Crushed stone aggregate – $15 – $45 per ton
- Landscaping stone – $40 – $100 per ton
- Slate roofing tiles – $250 – $1000 per square
- Granite blocks – $200 – $400 per cubic meter
- Granite slabs – $40 – $120 per square foot
- Basalt slabs – $30 – $70 per square foot
- Exotic dimension stone – Up to $1000 per square foot
Rare imported decorative stones like larvikite can command premium prices from luxury architects and designers. More common brown building stones like basic granite and slate are affordable for the average homeowner or contractor. The finished surface and rareness of the stone greatly impact the overall cost.
Conclusion
Identifying an unknown dark brown stone requires looking at key mineralogical and structural characteristics beyond just its color. Granite, basalt, schist, and slate are among the most common dark brown stones found in nature. They form through different geological processes but share similarities in appearance. Understanding the composition, grain size, texture, and possible uses of a stone helps properly identify it. Dark brown stones have important applications ranging from construction to decorative finishes. They originate from specific regions worldwide where unique varieties form, some becoming highly coveted for their beauty, durability, and rarity. With knowledge of their defining features, even amateur geologists can learn to accurately identify the many shades of brown stones.
