Key points
- Tourmaline is bright and beautiful, and comes in a rainbow of colours.
- The unique chemical composition of tourmaline gives it the ability to record its own geological history.
- Tourmalines have piezoelectric properties, so it can generate an electric charge under mechanical pressure.
Tourmaline, a crystalline silicate, comes in a kaleidoscope of colours. Depending on the elements present in its composition, this beautiful mineral can appear black, green, red, pink, or even exhibit a watermelon-like gradient from green to pink.
Research scientist Dr Mario Iglesias-Martinez is a passionate gemmologist whose work discovering and characterising critical minerals, unearths beautiful tourmaline specimens in lithium-bearing pegmatites.
Pegmatites are igneous rocks that are formed when magma crystallises.
“I’ve been fascinated by the diverse spectrum of colours found in tourmaline and its intricate zoning patterns, often found within a single crystal," Mario said.
"As a researcher, I’ve delved deeper into this mineral’s remarkable potential to capture the numerous processes that formed it, unveiling a multitude of geological events through its history."
Recording geological memories
Tourmaline’s ability to record geological data through its internal structure tells us a lot about geological processes, including volcanic eruptions.
"Some people have described tourmaline as a geological DVD; a home movie etched into its structure," Mario said.
Its recording ability comes down to tourmaline’s diverse chemical composition, resilience across varying geological environments, and remarkably slow diffusion rates—where atoms migrate from areas of high concentration to low concentration.
Piezoelectricity: electric under stress
Beyond their colourful home movies, tourmalines exhibit another fascinating physical property: piezoelectricity.
The structure of the crystals means that when mechanical stress is applied, they can generate an electric charge. This unique feature finds practical applications in many industries.
It is used in pressure-sensitive gauges and sensors, as it can detect tiny disturbances. It makes the sensors ideal for testing equipment and for medical imaging. They are also used in depth sounding instruments in submarines and devices for military equipment.
Interestingly, heat also causes the crystalline ends to polarise. Even warm sunlight can cause the crystal ends to charge and attract particles from the air, making them look dusty.
Not just pretty, tourmaline is useful
Tourmaline is sought after in the world of jewellery-making, where stones are highly prized for their many colours. And the global market is hungry for jewel-quality tourmaline. The star of the tourmalines is the neon green-blue coloured Paraiba variety. Exceptional specimens even rival diamonds in value.
But tourmaline is not just pretty. It’s a natural dynamo, permanently emitting negative ions and far-infrared radiation. This creates an electrostatic field and releases rare microelements. The result? A boost for microorganisms and plants, countering the effects of environmental pollution.
"Studies have also shown that tourmaline can activate gasoline and diesel," Mario said.
"Its far-infrared radiation can interact with carbon to carbon (C=C) bonds, enhancing fuel performance and reducing pollutants."
Largest library of mineral specimens
We are currently undertaking preliminary tourmaline investigations using data from the National Virtual Core Library (NVCL). This is the world’s largest drill core mineralogical database with data and imagery from sites across Australia. The NVCL's valuable information is freely available to users worldwide.
Our research captures the way light reflects off crystals, rock samples and drill cores. This information allows us to better understand the composition of geological material.
We’re creating a tourmaline database, spanning wavelengths from 350 to 14,500 nanometers, using Fourier-transform infrared spectroscopy.
“This method of spectroscopy gives us insights into the infrared absorption or emissions of various mineral samples,” Mario said.
Combine this with data from X-ray diffraction and other mineral analysis techniques, and geologists can make better use of information for mineral systems research.
"This can aid our discovery of pegmatites which are potential sources of lithium, tantalum, beryllium, and tin," Mario said.
Lithium is a critical mineral used widely in batteries for electronic devices and storage for renewable energy.
"If tourmaline is established as an indicator mineral (a mineral that indicates the presence of other minerals of interest), it could help prospectors efficiently target lithium-rich deposits. This will help with exploration accuracy and reduce time and cost," Mario said.