Garnet—An Essential Industrial Mineral and January’s 

Birthstone

	 	 	 arnet is one of the most 

 common minerals in the 

world. Occurring in almost any 

color, it is most widely known 

for its beauty as a gem stone. 

Because of its hardness and 

other properties, garnet is also an 

essential industrial mineral used 

in abrasive products, non-slip 

surfaces, and filtration. To help 

manage our Nation’s resources of 

such essential minerals, the U.S. 

Geological Survey (USGS) provides crucial data and scientific 

information to industry, policymakers, and the public.

G Photograph of a mineral 

specimen containing large 

crystals of the garnet 

mineral spessartine (red), 

showing the distinctive 

“euhedral isometric” 

crystal form of garnet. Used 

since ancient times for 

jewelry, the first industrial 

use of garnet was probably in coated sandpaper 

manufactured in the United 

States by Henry Hudson 

Barton in 1878. The United 

States currently consumes 

about 16 percent of the 

global production of industrial garnet. (Copyrighted 

photo by Stan Celestian/

courtesy of Glendale Community College).

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 2006–3149

2006

Garnet as a Gem Stone

Garnet is familiar to many people as 

January’s birthstone and as the New York 

State gem stone. It has been used as a gem 

stone since prehistoric times. Most recognizable in a deep shade of red, garnet occurs in 

the greatest variety of color of any mineral, 

except for blue. Some types of garnet even 

change color when exposed to artificial light. 

Unlike many other gem stones, garnet is 

almost never treated using heat, chemicals, 

or other methods to enhance appearance 

and value. The value of gem-stone garnets 

involves a complex combination of factors, 

including color, clarity, scarcity, durability, 

type of cut, and fashion. Larger garnets are 

popular both as gems and as collectable mineral specimens. Star garnets, found in Idaho, 

India, and Madagascar, contain inclusions of 

the fibrous mineral rutile that reflect light in 

two, four, or six rays when the stones are cut 

and polished. Star garnets with six rays are 

the rarest, and for about every 500 four-ray 

garnets only 1 six-ray garnet is found.

Garnet as an Industrial Mineral

The first industrial use of garnet appears to 

have been in coated sandpaper manufactured 

in the United States by Henry Hudson Barton 

in 1878. Garnet is an important industrial 

mineral because it is relatively hard, rating 6 

to about 8 on the “Mohs scale of hardness,” 

where diamond is the hardest at 10. Consequently, garnet is an excellent abrasive for 

applications such as sand- or air-blasting, 

water-jet cutting, and sandpaper. Garnet is 

now used for some blast-cleaning applications 

that previously used common sand. Common 

sand contains crystalline silica (SiO2) that in 

the form of dust produced during blasting can 

cause lung damage if inhaled.

There are many additional industrial 

applications of garnet, including conditioning aluminum and other soft metals for 

use in aircraft and ships; deburring welds 

and grinding and polishing optical lenses; 

producing high-quality, scratch-free semiconductor materials; finishing hard rubber, 

plastic, and wood products; and making nonskid paints and coatings. The U.S. petroleum 

industry is one of the leading garnet-consuming industries, using garnet for cleaning 

drill pipes and well casings. Garnet is also 

chemically inert and recyclable, making it an 

ideal filtration medium. 

Garnet can also be used in mining 

exploration as an indicator to help locate diamond deposits. Diamonds only form at great 

pressure and temperature and are associated 

with kimberlite, an intrusive igneous rock 

that comes from deep within the Earth. As 

the molten rock (magma) that cools to form 

a kimberlite rises toward the Earth’s surface, 

it incorporates fragments of rocks and minerals, including garnets with distinct color and 

composition that form under the same conditions as diamonds. If these distinct types 

of garnet are found in sediments, they may 

indicate the presence of nearby diamondbearing kimberlites.

How do Garnets Form?

Garnet crystals form in rocks of appropriate chemical composition that have been 

These cut and polished gem stones are a rare, 

green variety of andradite garnet, also known as 

“demantoid” garnet. Cut garnets are prized for their 

beauty and are also commercially valuable for use 

in jewelry. (Image courtesy of Peter Grumitt.)
modified by heat and pressure deep within 

the Earth’s crust. These are “metamorphic” 

rocks, such as gneiss, amphibolite, and 

schist. Less frequently, garnets form in 

“calcareous” rocks that have been heated 

by nearby intrusions of magma. 

Garnets can be recovered using either 

surface or underground mining methods. 

Most garnets are found in and recovered 

from alluvium (unconsolidated or poorly 

consolidated combinations of clay, silt, 

sand, and gravel) derived from metamorphic rocks that have undergone weathering 

and erosion. Subsequent stream action 

moves and deposits the garnets, resulting 

in local concentrations of garnet due to 

its high specific gravity (its mass relative 

to an equal volume of water). During the 

recovery process the specific gravity and 

magnetic properties of garnet are used to 

separate it from other material.

Are all Garnets the Same?

Although all garnets possess similar 

physical properties, including crystal structure, hardness, and specific gravity, there 

are actually several different types of the 

mineral. The six most common members 

of the garnet family are almandine (rich 

in iron and aluminum), grossular (rich in 

calcium), pyrope and spessartine (rich in 

magnesium or manganese), uvarovite (rich 

in chromium), and andradite (rich in iron). 

For more information contact:

James G. Evans

U.S. Geological Survey

904 W. Riverside Ave., Room 202

Spokane, WA 99201

Tel: (509) 368–3115 

http://minerals.usgs.gov

This Fact Sheet and any updates to it are available online at 

http://pubs.usgs.gov/fs/2006/3149/

James G. Evans, Phillip R. Moyle, David G. 

Frank, and Donald W. Olson

Edited by James W. Hendley II

Graphic design by Stephen L. Scott

This photo shows garnets of various grain sizes. Garnets are hard, chemically inert, and 

recyclable, making them ideal for industrial uses (see pie diagram). Garnets similar to 

those shown here are used in water-jet cutting, air-blasting, and filtration applications.

10%

other

35%

Abrasive

Blasting

30%

Waterjet

Cutting

15%

Water

Filtration

10%

Abrasive

Powders

Almandine is the hardest and, together 

with andradite, is the garnet mineral most 

commonly used in industrial applications. 

Tsavorite, a rare green grossularite garnet 

of exceptional beauty is among the most 

expensive garnets by weight. At the other 

extreme are reddish pyrope and abundant 

almandine garnets that are both common 

and relatively inexpensive.

Where are Garnet Deposits Found 

in the United States?

Garnet deposits have been located in 

21 different states, including Alaska, Arizona, California, Colorado, Connecticut, 

Idaho, Montana, Nevada, New Hampshire, 

New York, North Carolina, Pennsylvania, 

Utah, and Virginia. However, the only U.S. 

garnet mines currently active are in northern Idaho, southeastern Montana, and eastern New York. In Idaho, garnet deposits are 

found adjacent to metamorphic rocks that 

make up the western Clearwater Range. In 

Montana, garnet deposits are found in the 

Ruby Range and southern Tobacco Root 

Mountains. In both Idaho and Montana, 

garnets are mined from alluvial deposits 

that formed from weathering of amphibolite, mica schist, gneiss, or granite. In 

northeastern New York, garnet is mostly 

extracted from unweathered gneiss bedrock 

of the Adirondack Mountains using surface 

mining methods.

U.S. Industrial Consumption of 

Garnet

The United States presently consumes 

about 16 percent of the global production of 

industrial garnet. In 2005, domestic production of crude industrial garnet was 40,100 

metric tons (t), valued at $3.84 million. In the 

same year, the Nation imported 41,800 t of 

industrial garnet, valued at $5.91 million, primarily coming from Australia, Canada, India, 

and China. 

Meeting the challenge of supplying 

America’s needs for essential minerals such 

as garnet requires accurate and unbiased scientific data. The ongoing work of scientists 

with the USGS Mineral Resources Program 

provides the information crucial to the creation of sound policies that will ensure future 

supplies of mineral resources.

The Industrial Uses of Garnet

Printed on recycled paper

References

Evans, J.G., 2006, U.S. industrial garnet, in Bliss, 

J.D., Moyle, P.R., Long K.R., eds., 2002, Contributions to industrial-minerals research: 

U.S. Geological Survey Bulletin 2209-L 

[http://pubs.usgs.gov/bul/b2209-l].

Olson, D.W., 2005, Garnet, industrial: U.S. 

Geological Survey Minerals Yearbook 2005, 

p. 29.1-29.3 [http://minerals.usgs.gov/

minerals/pubs/commodity/garnet/index.

html#myb].

Hearn, B.C., and McGee, E.S., 1983, Garnets in 

Montana diatremes; a key to prospecting 

for kimberlites: U.S. Geological Survey Bulletin 1604, 42 p.

U.S. Bureau of Mines, 1995, An overview of production of specific U.S. gemstones [garnet]: 

U.S. Bureau of Mines Special Publication 

14-95 [http://minerals.er.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/

garnet.html].