Apatite: Mineral With Bite And Insight

Apatite. Rhymes with appetite, and fittingly, plays a vital role in the very act of eating. Found in our teeth and bones, apatite provides the structural strength behind every bite and step we take.

But this mineral is far more than a biological building block. It is an agricultural essential and geological timekeeper and storyteller.

Apatite (Ca₅(PO₄)₃(F,Cl,OH) is a group of calcium phosphate minerals. It also contains fluorine, chlorine and other trace elements like highly sought-after rare-earth elements (REEs). It reflects a variety of shades of green, blue, pink, yellow but can sometimes be transparent.

Feeding plant appetites

Beyond the human body, apatite plays a critical role in agriculture. It is the primary source of phosphorus, an essential nutrient for plant growth.

Phosphorus helps plants develop strong root systems, produce flowers and fruits, and increase overall yield.

Without it, modern agriculture would struggle to meet the demands of a growing global population. Apatite-derived phosphate fertilisers are thus indispensable to global food security.

An origin story of apatite

Geologically, apatite is formed through a variety of processes. It occurs in magmatic rocks, where it crystallizes from cooling magma. In sedimentary rocks it contributes to the cementation of sediments, and in metamorphic rocks it forms under intense pressure and/or temperature.

It is also found in quartz veins, and even in lunar and Martian meteorites, making it a mineral of both terrestrial and extraterrestrial significance.

Dr Coralie Siegel is a geologist who studies the behaviour of metals in magmatic and hydrothermal systems. She studies apatite to understand the timing of rock formation.

According to Dr Siegel, apatite's ability to form under diverse geological conditions makes it a valuable tool for investigating ore-forming systems and reconstructing geological histories.

"Because apatite forms under various conditions it can provide an insight into the mineralisation of different ore-forming systems," said Dr Siegel.

Dating rocks using geochronology

You've no doubt heard of carbon-14 dating. But have you heard of uranium-lead geochronology?

Geochronology is the science of determining the age of rocks, fossils, and sediments using natural radioactive decay.

Uranium-lead geochronology is one of the most robust and widely used radiometric dating methods in geology. This method can date minerals from millions to billions of years old.

Apatite is a timekeeper

"Apatite contains trace to moderate concentration of uranium (U) and lead (Pb) which allows the use of uranium-lead geochronology to determine the timing of crystallisation," said Dr Siegel.

Uranium-lead dating relies on the radioactive decay of uranium isotopes (²³⁸U and ²³⁵U) into lead isotopes (²⁰⁶Pb and ²⁰⁷Pb). Because these decay processes have well-known half-lives, measuring the ratio of uranium to lead in a mineral allows geologists to determine its age.

Using advanced equipment such as LA-ICP-MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry), researchers can precisely measure these concentrations.

Dr Siegel applied this technique to study apatite in magmatic nickel sulfides in the Eastern Goldfields of Western Australia , finding the deposit was formed about 2.4 billion years ago.

Recently, she has been studying apatite in gold-bearing quartz veins in the Victorian goldfields. Here the apatite minerals are younger, formed through hydrothermal events occurring around 160 million to 390 million years ago.

Australian geology is among the oldest on Earth, with parts of the continent dating back over 4.4 billion years and is rich in mineral resources, including gold, nickel, iron ore, rare earth elements and other critical minerals

"Apatite helps us understand the signatures and timing of hydrothermal activity and mineralisation events, " Dr Siegel explained.

"This information helps us in our hunt to discover deposits of the critical commodities we all rely on."