Category: Minerals


Barite Minerals

Barite

The nonmetallic mineral with an incredible specific gravity. Article by: Hobart M. King, Ph.D., RPG Barite: Barite from Kings Creek, South Carolina. Specimen is approximately 4 inches (10 centimeters) across. What is Barite? Barite is a mineral composed of barium sulfate (BaSO 4 ). It receives its name from the Greek word "barys" which means "heavy.

Read More
Hornblende Minerals

Hornblende

A common rock-forming mineral found in igneous and metamorphic rocks Article by: Hobart M. King, Ph.D., RPG Hornblende: Hornblende with a typical black granular to fibrous appearance from Faraday Township, Ontario, Canada. This specimen is approximately 3 inches (7.6 centimeters) across. What is Hornblende?

Read More
Herkimer Diamonds Minerals

Herkimer Diamonds

Doubly terminated quartz crystals named for Herkimer County, New York Article by: Hobart M. King, Ph.D., RPG Herkimer Diamond Quartz Crystals Vuggy rock with drusy quartz, hydrocarbon and a nice Herkimer Diamond. Rock is 6" across. Click here for a larger image, or zoom in for detail. What are Herkimer Diamonds?

Read More
How Do Diamonds Form? Minerals

How Do Diamonds Form?

Contrary to what many people believe, diamonds do not form from coal. Article by: Hobart M. King, Ph.D., RPG Diamond formation: Diamonds found at or near Earth's surface have formed through four different processes. The plate tectonics cartoon above presents these four methods of diamond formation. Additional information about each of them can be found in the paragraphs and small cartoons below.

Read More
Arsenopyrite Minerals

Arsenopyrite

Mineral Properties and Uses Article by: Hobart M. King, Ph.D., RPG Arsenopyrite and milky quartz on limestone from the Smith Vein, Carrock Mine, Caldbeck Fells, Cumberland, Cumbria, England. Specimen is approximately 8.8 x 6.2 x 4.8 centimeters in size. Specimen and photo by Arkenstone / www.iRocks.com.

Read More
Gold Minerals

Gold

Mineral Properties and Geologic Occurrence Article by: Hobart M. King, Ph.D., RPG Gold Nuggets from Colorado. These specimens range between three and eight millimeters across. They have the uniform color and rounded edges common of alluvial gold particles. What is Gold? Native gold is an element and a mineral.

Read More
Rutile Minerals

Rutile

A source of titanium, a white pigment in paint, a cause of “eyes” and “stars” in gems. Article by: Hobart M. King, Ph.D., RPG Rutilated Quartz: A tumbled stone of rutilated quartz. Rutile can occur as needle-shaped crystals in minerals such as quartz, corundum, garnet, and andalusite. Image copyright iStockphoto / Coldmoon_photo.

Read More
Carbonado Diamonds Minerals

Carbonado Diamonds

The same hardness, but much tougher than other varieties of diamond. Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Carbonado Diamonds are usually black or gray in color and irregular in shape. Upon close examination, their porous texture is usually obvious. They typically exhibit a luster that might be perceived as glassy, submetallic, or adamantine.

Read More
Marcasite Minerals

Marcasite

Mineral Properties and Uses Article by: Hobart M. King, Ph.D., RPG Cockscomb Marcasite: Tabular crystals of “cockscomb” marcasite with spear tip terminations, grown on a base of fluorite. This specimen was collected from the Denton Mine, a fluorite producer in Illinois. It measures about 4.1 x 2.0 x 2.

Read More
Chromite Minerals

Chromite

The only ore of chromium, the metal used to make stainless steel, nichrome, and chrome plating. Article by: Hobart M. King, Ph.D., RPG Chromite: Chromite from the Transvaal area of South Africa. Specimen is approximately 4 inches (10 centimeters) across. What is Chromite? Chromite is an oxide mineral composed of chromium, iron, and oxygen (FeCr 2 O 4 ).

Read More
Epidote Minerals

Epidote

Epidote is a metamorphic mineral and the name of a silicate mineral group. Article by: Hobart M. King, Ph.D., RPG Epidote: Epidote from Rockbridge County, Virginia. This specimen is approximately 4 inches (10 centimeters) across. What is Epidote? Epidote is a name that is used in two different ways in mineralogy: 1) the "Epidote Group" is the name of a group of silicate minerals that share common structural and compositional characteristics; and, 2) "Epidote" is the name of the most common mineral in the Epidote Group.

Read More
Brown Diamonds Minerals

Brown Diamonds

Also known as chocolate, champagne or cognac diamonds Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Beautiful Brown Diamonds: Three cognac-colored diamonds from Rio Tinto's Argyle mine in Western Australia clearly demonstrate the beauty of brown diamonds. Image Copyright 2016 Rio Tinto. Table of Contents What Are Brown Diamonds?

Read More
Limonite Minerals

Limonite

An amorphous iron oxide used as an ore of iron and as a pigment for thousands of years. Article by: Hobart M. King, Ph.D., RPG Limonite: A specimen of iridescent, botryoidal limonite from Guangxi, China. Specimen is approximately 15 x 9 x 5 centimeters. Specimen and photo by Arkenstone / www.iRocks.com.

Read More
Quartz Minerals

Quartz

A ubiquitous mineral with an enormous number of uses Article by: Hobart M. King, Ph.D., RPG Quartz crystals: Herkimer "Diamond" quartz crystals. A clear, "rock crystal" variety of quartz. What is Quartz? Quartz is a chemical compound consisting of one part silicon and two parts oxygen. It is silicon dioxide (SiO 2 ).

Read More
Andalusite and Chiastolite Minerals

Andalusite and Chiastolite

Article by: Hobart M. King, Ph.D., RPG Andalusite: A scatter of faceted andalusite. If you look closely at these gems, you can see that many of them appear to be composed of a mosaic of color. This is an expression of the strong pleochroism of andalusite. Image by cobalt123, used here under a Creative Commons license.

Read More
Is Water a Mineral? -- Is Ice a Mineral? Minerals

Is Water a Mineral? -- Is Ice a Mineral?

The best way to find out is to compare their properties to the definition of the word "mineral." Article by: Hobart M. King, Ph.D., RPG Hubbard Glacier: Photograph of the Hubbard Glacier calving into Disenchantment Bay near Seward, Alaska. Image copyright iStockphoto / MaxFX. What is a Mineral? The word "mineral" is used by geologists for a group of naturally occurring crystalline substances.

Read More
Fluorite (also known as Fluorspar) Minerals

Fluorite (also known as Fluorspar)

An important industrial mineral used in many chemical, ceramic, and metallurgical processes. Article by: Hobart M. King, Ph.D., RPG Fluorite: This photo shows several beautiful blue cubic crystals of fluorite with occasional pyrite crystals on their faces. Fluorite is commonly found as cubic crystals, but blue crystals are unusual.

Read More
Crystal Habits and Forms of Minerals and Gems Minerals

Crystal Habits and Forms of Minerals and Gems

Article by: Hobart M. King, Ph.D., RPG Acicular Acicular crystals have a needle-like shape that tapers to a point or a blunt termination. Many acicular crystals can be clustered to produce fan-shaped or radially-shaped aggregates. The name acicular should be used when the length of an individual crystal is much greater than its width or diameter.

Read More
Euclase Minerals

Euclase

A rare beryllium mineral, sometimes cut as a collector's gem Article by: Hobart M. King, Ph.D., RPG Euclase Crystal: A beautiful blue crystal of euclase with a nice termination and obvious striations. This specimen measures approximately 2.1 x 1.3 x 0.3 centimeters in size and is from Gachala, Boyaca Department, Colombia.

Read More
Magnesite Minerals

Magnesite

Used to make inexpensive gems, chemicals, fire bricks, magnesium metal and more. Article by: Hobart M. King, Ph.D., RPG Crushed Magnesite: Heated to produce magnesium oxide that is used as a raw material for the chemical industry, a refractory material for the steel industry, and as a minor source of magnesium metal.

Read More