U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2007–3056

August 2007

USGS Reference Materials Program

Serving the needs of the global analytical community

Printed on recycled paper

Introduction

Every year in the United States, millions of measurements 

are made on the chemical composition of items that affect us on 

a daily basis. The accuracy of these measurements is routinely 

determined by the analysis of appropriate reference materials. 

The composition of these reference materials has been previously 

determined through rigorous testing by multiple laboratories 

using a variety of analytical techniques. Today, reference 

materials help to accurately evaluate the composition of our 

food, water, air, the medicines we use, the soil we grow our 

crops in, and hundreds of other products that affect our everyday lives.

In the field of earth science, reference materials are very 

important because they help us develop a better understanding 

of the processes that have shaped, and continue to shape the 

world around us. Despite the importance of geological reference 

materials, a little more than four decades ago reliable reference materials for silicate rocks were unavailable. However, in 

1951 the Massachusetts Institute of Technology (MIT) and the 

U.S. Geological Survey (USGS) cooperated to develop reference materials G-1 (granite) and W-1 (diabase)—producing 

the first readily available supply of well-characterized silicate 

rock materials. This early effort has since led to the development of 42 additional reference materials ranging from soils, 

to marine sediments, manganese nodules, and a host of 

diverse silicate rocks in support of USGS programs. At present, 

USGS reference materials are distributed internationally to 

organizations involved in geochemical and environmental 

analysis, instrumentation and methods development, and industrial research and quality assurance. In addition, the reference 

materials are widely used in the development and validation of 

geochemical models used by the USGS. Since the program’s 

inception, more than 20,000 units of USGS reference materials 

have been distributed.

How Reference Materials Are Used

Reference materials are used by a variety of government, 

private, and university laboratories around the world in 

the development and validation of analytical measurement 

methodologies. The reliability of new analytical techniques 

is routinely verified by the analysis of appropriate reference 

materials, for which accurate values are known. This process rigorously evaluates the method’s ability to produce 

accurate results.

Another important use of reference materials is in a 

laboratory’s quality control program. A laboratory quality 

control program routinely evaluates a laboratory’s analytical 

accuracy based on the analysis of “blind” reference materials 

(where the laboratory does not know the samples are reference 

materials). In these cases, reference materials that closely 

USGS Geochemical Reference Materials are natural matrix 

materials that have been well characterized for their chemical 

composition.

USGS reference materials are used by a variety of government, 

private industrial, and university laboratories.

Industrial

44%

Government

16%

University

40%
Once a need is established (for example, “trace elements 

in shale”), potential collection sites are identified using 

information from the USGS National Geochemical Database 

and other sources, followed by a field trip to the site to collect test samples. Generally, the starting material is a natural 

geologic deposit from a location in the United States which 

meets the general composition requirements—this is where 

the reference materials produced by the USGS are unique 

compared to those from many other suppliers. If analysis of the 

test samples indicates that the material is suitable, the site is 

revisited for full-scale collection activities. A sufficient quantity 

of the material is then harvested and brought back to the USGS 

laboratory in Denver, Colorado. In the laboratory, as much as 

1,000 pounds of base material is pulverized and ground into 

a fine powder. The finely ground powder is mixed to ensure 

homogeneity and then split into individual 30–100 gram bottles 

using a custom-designed spinning riffler sampling device. The 

natural matrix reference material is then labeled and put into 

storage. Due to the labor-intensive nature of producing, analyzing, and certifying a new reference material, it is USGS policy 

to produce enough material to last a minimum of 20 years. 

This approach allows scientists to monitor long-term trends 

in chemical analysis, provides the community with wellcharacterized materials that are important links to historical 

studies, and allows for reliable intra-laboratory comparisons 

of new techniques.

In the past several years, an increased interest in direct 

trace elemental analysis of solids at the micrometer scale 

using Laser Ablation ICP-MS and Electron/Ion Microprobe 

analysis has brought a new set of challenges to the field of 

reference material development. In order to calibrate these 

Scientists worldwide use USGS reference materials to validate 

analytical methods and check instrument performance.

Steve Wilson (USGS, Denver) collecting base material to be used 

in the preparation of a new reference material.

Other

3% Australia

5%

Canada

11%

Europe

21%

Asia

8%

India

3%

USA

49%

match actual sample compositions are important in order to 

evaluate the laboratory’s performance on real samples. In addition, many scientists submitting samples to either commercial 

or in-house laboratories may include reference materials in with 

their samples as an immediate check on laboratory accuracy.

Because many different analytical techniques are used 

to determine the “certified value” of the reference material, 

the reference materials can be used in a wide variety of 

analytical techniques, including those that perform direct sample analysis, such as XRF (X-ray fluorescence spectroscopy) 

and INAA (instrumental neutron activation analysis), as 

well as those that require the sample to be prepared in some 

manner (usually via an acid digestion) such as ICP-OES 

(inductively coupled plasma optical emission spectroscopy) 

or ICP-MS (inductively coupled plasma mass spectrometry). 

The geochemical reference materials produced by the USGS 

are utilized by scientists throughout the world to validate their 

methods and procedures.

As new techniques are developed and we continue to 

perform more measurements on substances that affect our 

everyday lives, the use of reference materials has steadily 

increased. During the last 10 years, the number of USGS 

reference materials shipped to users has increased, on average, 

by 14 percent annually—indicating a growing need for reference materials.

Preparation of Reference Materials

The exact procedures for making reference materials vary, 

depending on the starting materials and the final physical form 

of the reference material. The first step is to identify what type 

of material is needed and what elemental content it should have. 

Generally, the need for a new reference material is identified 

through requests from public and private sector groups as well 

as by USGS and other government agency scientists.
instruments, a new generation of reference materials is 

required with element homogeneity at the micrometer scale. 

This micro-homogeneity requirement generally cannot be 

achieved using conventional powdered materials. In addition, 

these new materials must be prepared in sufficient quantities 

to allow for the generation of long-term intra-laboratory data 

for method validation.

microanalytical reference materials are produced as pellets that 

will fit in a standard laser ablation chamber. In addition, microanalytical reference materials have been developed with compositions similar to coral (MACS series), bone (MAPS series), 

polymetallic sulfides (MASS series), and wood/organic materials 

(MAOS series). These materials are currently used extensively in 

environmental studies as well as investigations into ore deposit 

formation. Additional materials produced by this method are 

currently under development.

Once a new standard has been prepared, it must be analyzed 

and certified before it can be distributed. Samples of the new standard are sent to a select group of USGS, government, academic, 

and private laboratories for analysis. The laboratories are selected 

by their ability to perform high-quality analyses using a variety of 

analytical techniques, including NAA (neutron activation analyses), TIMS (thermal ionization mass spectrometry), ICP-OES, 

ICP-MS, and other specialized techniques. When the results from 

these analyses are received, they are tabulated and statistically 

analyzed to obtain the certified concentration value for each component. The certificate is prepared and the reference material is 

then ready for shipment. The entire development process can take 

as long as 1 year to produce a new reference material.

The spinning riffler sampler fills bottles with prepared reference 

material.

Visiting scientist from Brazil working on a new reference material.

Microanalytical basaltic glass reference materials for Laser Ablation 

ICP-MS calibration, mounting disks, and laser sample holders.

The USGS has developed two innovative approaches for 

preparing microanalytical reference materials—reaffirming the 

USGS as a leader in solid reference material development for 

the global scientific community. In the first approach, a powdered 

material is melted in a high-temperature furnace and then flashcooled to prevent crystallization. The resulting glass-like material 

retains the same chemical composition as the starting material, 

and the resulting homogeneity at the 10–20 micrometer scale is 

sufficient to meet the demands of many microanalytical procedures. The resulting solid material is then reduced to pieces of a 

suitable size and then mounted into a support substrate. This type 

of reference material is in increasing demand by the analytical 

community for calibrating instrumentation.

When no natural materials exist with sufficient micro-scale 

homogeneity or a material cannot be converted to the glassy 

form, other avenues for generating solid reference materials are 

explored. In a second approach, a chemical precipitation procedure is used to produce a synthetic material with a well-defined 

elemental composition at predetermined concentrations. Using 

this procedure, the USGS has developed a series of matrixspecific microanalytical reference materials with a homogeneity and trace-element chemistry suitable for calibrating Laser 

Ablation ICP-MS instrumentation. These precipitated powder 
Currently Available Reference Materials

The majority of USGS reference materials are based 

on silicate rocks that were collected from the continental 

United States and Hawaii. These reference materials range in 

composition from basalt to shale. The selection of reference 

materials available has diversified through time in response to 

changes in USGS needs, requests from other government agencies, and inquiries from public sector scientists. This diversification is driven by the need to match reference materials with 

sample type. For example, requests from the oceanographic 

community led to the development of a deep-ocean marine 

sediment and two manganese nodule reference materials. 

Inquiries from the mining industry initiated the development of 

several geochemical exploration standards (GXR series) that are 

widely used to help in the discovery of various ore deposits. In 

response to specific environmental studies, the USGS has developed a freshwater-sediment reference material that has a high 

concentration of extractable selenium. This reference material is 

useful in western agricultural studies where selenium in agricultural runoff can be a significant environmental issue. Currently, 

the production of microanalytical reference materials for use 

with direct solid sampling techniques, such as Laser Ablation 

ICP-MS, and the replacement of depleted reference materials 

are among the priorities of the reference materials program.

Partial listing of USGS Geochemical Reference Materials 

available. See website for complete listing and more information.

co-producing numerous reference materials ranging from soils 

to marine sediments to an industrial sludge. The USGS reference 

materials program has also assisted other countries in the development of standards. Most recently, the USGS assisted Brazilian 

scientists in the preparation of a basalt reference material for 

geochemical analysis.

Future Needs and Directions

As new analytical techniques develop, new reference 

materials will be needed in order to validate methods, calibrate 

instrumentation, and ensure production of quality data. New 

direct solid analysis techniques such as Laser Ablation ICP-MS 

and Laser Induced Breakdown Spectroscopy (LIBS) will require 

solid reference materials for use in instrument calibration and 

verification. As the responses obtained for each element by 

these direct analysis techniques can vary greatly depending 

on the concentrations and identity of matrix elements present, 

matrix-specific reference materials will be necessary.

With continuing studies of the Earth and how the effects 

of our interactions with it impact our everyday lives, scientists 

have come to realize that determining the total concentration 

of an element is not enough. The interactions that can occur 

between an element and the environment or a living organism 

will depend on the chemical form of the element; thus, determining which elemental species are present is also important. 

As these speciation analyses (the determination of the form of 

an element present in a sample, such as hexavalent chromium 

or trivalent chromium) become more routinely used, solid 

geochemical reference materials with specific element species 

concentration information will be necessary for developing and 

validating analytical methods.

The use of reliable reference materials by the public and 

private sectors will continue to expand and be an integral part 

of international efforts to standardize analytical techniques now 

and in the future. In response to this global need, the USGS 

Reference Materials Program will continue to produce relevant 

and well-characterized natural matrix geologic reference materials that will lead to more accurate scientific analyses.

Contact Information

For more information regarding the USGS 

Reference Materials Program, please see our website at: 

http://minerals.cr.usgs.gov/geo_chem_stand/index.html

or contact:

Dr. Stephen A. Wilson

U.S. Geological Survey

Box 25046, MS 964D

Denver Federal Center

Denver, CO 80225

Tel: 303-236-2454

e-mail: (swilson@usgs.gov)

Written by Ruth E. Wolf and Stephen A. Wilson

Powdered Geochemical Reference Materials

AGV-2 Andesite GSP-2 Granodiorite

BCR-2 Basalt NOD-A-1 Mn Nodule

BHVO-2 Basalt NOD-P-1 Mn Nodule

BIR-1 Basalt SDC-1 Mica Schist

COQ-1 Carbonatite QLO-1 Quartz Latite

CLB-1 Coal SGR-1 Shale

SDO-1 Oil Shale SCo-1 Cody Shale

DNC-1 Dunite W-2A Diabase

RGM-2 Rhyolite BSK-1 Sediment

Microanalytical Reference Materials

MACS-1 coral matrix BIR-1G basalt glass

MAPS-1 bone matrix GSA-1G synthetic glass

MASS-1 sulfide matrix GSC-1G synthetic glass

MAOS-1 organic matrix GSD-1G synthetic glass

BCR-2G basalt glass GSE-1G synthetic glass

BHVO-2G basalt glass

In addition to the development of our own reference 

materials, the USGS assists other Federal agencies in the preparation of specific reference materials. The Environmental Protection 

Agency (EPA) has utilized the expertise of the USGS in order to 

develop proficiency samples used to evaluate laboratory analysis 

of asbestos in soils. The National Institute for Standards and 

Technology (NIST) has made extensive use of USGS capabilities,