[Diffuse Reflectance Spectroscopy of Red Colored “Laowo Stone”]

Area of Science:

• Mineralogy
• Geochemistry
• Materials Science

Background:

• Laowo Stone from Laos is a new seal stone impacting the Chinese market.
• The coloration mechanism of Laowo Stone remains unclear.
• Understanding the coloration is crucial for market value and identification.

Purpose of the Study:

• To investigate the coloration mechanism of red Laowo Stone.
• To identify the specific minerals responsible for the red color.
• To establish a relationship between elemental composition and color intensity.

Main Methods:

• X-ray Diffraction (XRD) and Fourier-Transform Infrared Spectroscopy (FTIR) for mineral identification.
• Energy Dispersive X-ray Fluorescence (EDXRF) for elemental analysis.
• Visible Diffuse Reflectance Spectroscopy (DRS) to detect iron minerals and their concentration.

Main Results:

• Laowo Stone's primary mineral is dickite, with minor kaolinite.
• Red coloration strongly correlates with iron (Fe) content; deeper red indicates higher Fe.
• Diffuse Reflectance Spectroscopy (DRS) identified hematite as the coloring agent, with a characteristic peak at 565-570 nm in the first-order derivative spectrum.

Conclusions:

• The red coloration of Laowo Stone is attributed to the presence of minute hematite crystals.
• These hematite crystals are dispersed within the grain boundaries of the dickite particles.
• The study clarifies the coloration mechanism, aiding in the identification and valuation of Laowo Stone.