An essential and very important aid for the observation of internal features of gemstones. The inclusions of certain minerals or gemstones are very typical for its geographical origin. By using a microscope, heat-treatments and other clarity enhancements can be identified.
A ratio, which indicates the ‘optical density’ of a substance. It is related to the angles of incidence and refraction of light. The refractive index is different for most gem-species.
Specific Gravity (SG) is the ratio of the weight of a substance to the weight of an equal volume of water. Every gem has its own specific gravity and the SG can be used as an additional value in gemstone identification. For this, a hydrostatic balance is used.
An optical instrument used in testing transparent gemstones to distinguish between isotropic and anisotropic materials.
An instrument for detecting pleochroism in a material. It is constructed so that two pleochroic colours, or shades of colour, can be detected and compared side by side in a single view.
GRC uses several different 3-digit carat balances (Mettler Toledo auto calibration carat balances).
FTIR spectrometers are used to measure absorption in
materials within the infrared part of the electromagnetic
spectrum. In infrared spectroscopy, IR radiation is passed
through a sample. Some of the infrared radiation is absorbed
by the sample and some of it is transmitted. The resulting
spectrum represents the molecular absorption and
transmission, creating a molecular fingerprint of the
sample. Like a fingerprint no two unique molecular
structures produce the same infrared spectrum. This makes
infrared spectrometry very useful for several types of
analysis. For example to:
Detect polymers, oils and resins used for impregnation, e.g. in jadeite, opal or emerald
Distinguish certain natural and synthetic gem materials, e.g. emerald
Opinions on heat treatment on ruby and sapphire
Raman spectroscopy is used to study vibrational, rotational,
and other low-frequency modes in gemstones and minerals. It
relies on inelastic scattering, or Raman (Raman effect)
scattering, of monochromatic light, from a laser in the
visible, near infrared, or near ultraviolet range. The laser
light interacts with molecular vibrations, phonons or other
excitations in the system, resulting in the energy of the
laser photons being shifted up or down. The shift in energy
gives information about the vibrational modes in the system.
Raman spectrometry is a very fast and reliable tool for the
identification of minerals and gemstones. Raman spectrometry
is used to:
Identify gem materials or individual parts of a gem or ornamental object
Identify filling substances e.g. resins and oils in emerald
Photoluminescence (abbreviated as PL) is light emission from
any form of matter after the absorption of photons
(electromagnetic radiation). It is one of many forms of
luminescence (light emission) and is initiated by photo
excitation (excitation by photons), hence the prefix photo-.
The photoluminescence systems are used to:
Distinguishing between natural and synthetic diamonds
Identification of diamond treatments
Identification of minerals
Identification of gemstone treatments
UV spectrometers are used to measure and record
characteristic absorption patterns within the UV radiation
range of the gemstone. The UV-VIS spectrometer is used to:
Investigate the origins of emeralds and sapphires, where stones of certain different origins may produce different absorption characteristics in the UV and visible regions of the spectrum
Identification aid for minerals
Energy dispersive X-ray fluorescence Spectrometry is used to
analyze the chemical composition of a gemstone. A sample is
targeted by high-energy X-ray, Inner orbital electrons are
ejected by high energy (short-wavelength) X-rays. This
removal results in an unstable atom structure leading to
electrons from higher orbital’s to fall back into the
position of the ejected electron. The energy difference
between the original and final orbital is released in the
form of characteristic X-rays (fluorescence). Energy and
number of these characteristic X-rays are transformed into a
spectrum. Each peak being characteristic of a chemical
element of a particular atom number. The relative
concentrations of elements is indicated by the fluorescent
X-ray peak intensities. EDXRF is used to distinguish:
Natural from synthetic gem materials
The origin of gemstones by indicating the relative concentration of certain elements
A short laser pulse is focused on to the surface of a
gemstone to create a plasma. Emissions from the atoms and
ions in the plasma are collected and analyzed by a high
resolution spectrometer. LIBS is used to:
Test corundum for beryllium treatments and semiquantitave analysis of light elements: Li, Mg and Be in gemstones.
The potential origin of a gemstone by detecting certain elements
In Laser Ablation Inductively Coupled Plasma Mass
Spectrometry the gemstone or mineral is directly analyzed by
ablating with a pulsed laser beam. The created aerosols are
transported into the core of inductively coupled argon
plasma (ICP), which generates a very high temperature. The
plasma in ICP-MS is used to generate ions that are then
introduced to the mass analyzer. These ions are then
separated and collected according to their mass to charge
ratios. LA-ICP-MS is used to:
Analyze the constituents of an gemstone, mineral or unknown sample. They can be identified and measured, even very light elements.