soil how to identify kimberlite

3 min read 25-02-2025

Kimberlite is a rare, igneous rock known for its potential to contain diamonds. Identifying kimberlite requires a keen eye and understanding of its unique characteristics. This guide will help you learn how to spot this valuable rock in the field.

What is Kimberlite?

Kimberlite is a type of ultramafic rock formed by volcanic eruptions deep within the Earth's mantle. These explosive eruptions bring fragments of the mantle, including diamonds, to the surface. Because of its deep origin, kimberlite possesses a unique mineralogical composition and texture.

Key Characteristics of Kimberlite

Identifying kimberlite isn't always straightforward. However, several key characteristics help distinguish it from other rocks:

1. Texture and Appearance

Kimberlite typically has a distinctive texture: it's often described as a "breccia," meaning it's composed of angular fragments of various minerals cemented together. The color can vary, ranging from dark greenish-gray to almost black. It often shows a somewhat porous or fractured appearance.

2. Mineralogical Composition

Kimberlite contains a unique suite of minerals, some of which are diagnostic. These include:

Olivine: A common mineral in kimberlite, often appearing as yellowish-green crystals.
Serpentine: A greenish alteration product of olivine, often abundant in weathered kimberlite.
Phlogopite: A type of mica with a bronze or brownish-yellow color.
Carbonate minerals (calcite, dolomite): These can be present in significant amounts.
Diopside: A green pyroxene mineral.

The presence of these minerals, especially in combination, strongly suggests kimberlite. However, keep in mind that not all kimberlites contain all these minerals.

3. Secondary Characteristics

Weathering plays a significant role in kimberlite's appearance. Exposed kimberlite pipes often show significant alteration, leading to changes in color and texture. Look for:

Yellowish-brown to reddish-brown staining: Caused by iron oxides from weathering.
Clay-rich alteration zones: These form as primary minerals break down.

4. Field Setting

Kimberlite pipes are typically cylindrical or pipe-shaped. They often stand out in the landscape due to their resistance to erosion. They’re often found in cratons (old, stable parts of continents).

Distinguishing Kimberlite from Other Rocks

Several rocks might resemble kimberlite, causing confusion. Careful observation and analysis are crucial to avoid misidentification. Key differences include:

Basalt: While both are dark-colored volcanic rocks, basalt generally lacks the characteristic breccia texture and mineral assemblage of kimberlite.
Lamproite: Lamproites are another type of ultramafic rock that can contain diamonds. However, they typically have a different mineralogical composition than kimberlite.
Other Mafic Rocks: Many mafic and ultramafic rocks share some similarities with kimberlite. Microscopic examination is crucial to make a definitive identification.

How to Identify Kimberlite: A Step-by-Step Approach

Observe the rock's texture and color: Look for a brecciated texture, dark color, and possible alteration.
Examine the minerals present: Look for olivine, serpentine, phlogopite, and other characteristic minerals using a hand lens if available.
Consider the geological setting: Is it located within a known craton? Does it show pipe-like morphology?
If possible, collect a sample for laboratory analysis: Thin sections under a petrographic microscope provide definitive identification.

Caution: Professional Identification is Crucial

While this guide provides helpful information, positively identifying kimberlite requires expertise. Always consult with a geologist or gemologist for confirmation, particularly if you suspect you've found a diamond-bearing kimberlite. Misidentification could lead to wasted time and resources.

Identifying kimberlite is a complex process that combines field observation and laboratory analysis. This guide provides a starting point for understanding the key characteristics of this fascinating and economically significant rock.