How does geochemistry reveal the chemical composition of rocks?

Geochemistry reveals the chemical composition of rocks by applying advanced analytical techniques to identify and quantify the elements and isotopes present within geologic materials. These methods allow scientists to determine both the bulk composition of a rock and the specific makeup of individual minerals.12

Key analytical instruments include:

• X-ray fluorescence (XRF) spectrometer: This device bombards a rock sample with X-rays, causing it to emit secondary fluorescent radiation. Because each element produces a diagnostic X-ray intensity proportional to its concentration, this method is highly effective for calculating the bulk composition of rocks.12
• Electron microprobe: By focusing a beam of electrons on a thin, microscopic slice of a mineral, this tool can determine the chemical composition of specific minerals almost instantly.12
• Inductively coupled plasma (ICP) spectrometer: This method involves dissolving a rock sample into a solution and introducing it into a plasma. The concentration of elements is then determined by measuring the light emitted, making it ideal for analyzing large numbers of samples.1
• Mass spectrometry: This technique sorts gaseous ions based on their mass-to-charge ratios, allowing for the identification of isotopes and the precise measurement of their abundances. Advanced versions, such as the Inductively Coupled Plasma Mass Spectrometer (ICP-MS), are used to determine the isotopic ages of minerals like zircon and titanite.34
• Neutron-activation analysis: By bombarding samples with neutrons, this method creates unstable radionuclides that emit diagnostic radiation, which is particularly useful for measuring rare earth elements with high precision.1