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.
Called "brown mica" after its color, "magnesia mica" after its composition. Article by: Hobart M. King, Ph.D., RPG Barrel-Shaped Phlogopite Crystal and small phlogopite flakes in white marble. Cleavage steps can be seen on the top of the crystal. This specimen was collected from Franklin, New Jersey and measures 8.
Also known as lab-created diamonds, man-made diamonds, synthetic diamonds. Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Synthetic Diamonds grown in the High-Temperature Materials Laboratory of the Moscow Steel and Alloys Institute. Photo by Wikipedian Lidvig14, used here under a Creative Commons Attribution-ShareAlike 3.
Records for both rough and faceted diamonds. Author: Hobart M. King, Ph.D., GIA Graduate Gemologist The Cullinan Diamond: A photograph of the Cullinan Diamond being held by Frederick Wells, who discovered it while working as the surface manager of the Premier Mine. This photo was taken in 1905 by an unknown photographer.
Used as a gemstone for over 2000 years. Today it is the primary ore of zirconium. Article by: Hobart M. King, Ph.D., RPG Zircon Crystal: A small cluster of nicely-formed zircon crystals which clearly demonstrate that zircon is a member of the tetragonal crystal system. The four-sided crystals are prismatic with a square cross-section and terminate with a pyramid.
A pink to purple mica, a source of lithium, an ornamental stone, a gem material. Article by: Hobart M. King, Ph.D., RPG Lepidolite Mica: This photo shows how lepidolite mica occurs in stacks of sheets, sometimes referred to as "books". This photo also shows a typical purplish pink color exhibited by the mineral, its perfect cleavage in one direction, and its pearly to vitreous luster.
A rapid hardness test for field and classroom use Article by: Hobart M. King, Ph.D., RPG Mohs Hardness Kit: A laboratory Mohs Hardness Scale kit containing: (1) talc; (2) gypsum; (3) calcite; (4) fluorite; (5) apatite; (6) orthoclase; (7) quartz; (8) topaz; and (9) corundum. Diamond is not included in most kits to keep the cost down.
Extremely rare and can fetch prices of over $1 million per carat. Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Argyle Isla: The Argyle Isla is a 1.14-carat Fancy red radiant-cut diamond mined from the Argyle Mine in Western Australia. It is one of the most valuable diamonds in the world on the basis of dollars per carat.
A group of rock-forming minerals found in Earth's crust. An abundant mineral in Earth's mantle. A constituent of many meteorites. Article by: Hobart M. King, Ph.D., RPG Olivine in basalt: Lherzolite (a variety of peridotite) nodules in a xenolith collected from a basalt flow at Peridot Mesa, Arizona.
Interesting materials that fall short of meeting the definition of a "mineral" Article by: Hobart M. King, Ph.D., RPG Common opal is a mineraloid. It is an amorphous silica with a chemical composition of SiO 2 . nH 2 O. It has a conchoidal fracture that is characteristic of an amorphous glass. Precious Opal is a mineraloid.
Article by: Hobart M. King, Ph.D., RPG Gold in jewelry: Cameo in gold setting. Image copyright iStockphoto / Angelo Marcantonio. The Most Useful Metal Of all the minerals mined from the Earth, none is more useful than gold. Its usefulness is derived from a diversity of special properties. Gold conducts electricity, does not tarnish, is very easy to work, can be drawn into wire, can be hammered into thin sheets, alloys with many other metals, can be melted and cast into highly detailed shapes, has a wonderful color and a brilliant luster.
Properties, uses, and occurrence of the most important ore of iron. Article by: Hobart M. King, Ph.D., RPG Oolitic Hematite: A specimen of oolitic hematite iron ore. Oolites are tiny round spheres of chemically precipitated hematite. The specimen in the photo is about four inches (ten centimeters) across, and the largest oolites are a few millimeters in diameter.
A pink to red manganese silicate used as a gemstone and minor ore of manganese. Article by: Hobart M. King, Ph.D., RPG Rhodonite from Nevada: Rhodonite with its characteristic matrix and fracture-filling of manganese oxide. This specimen from Humboldt County, Nevada was photographed by Chris Ralph of Nevada-Outback-Gems.
A pink manganese carbonate mineral used as an ore, a gemstone, and a crystal specimen. Article by: Hobart M. King, Ph.D., RPG Rhodochrosite: Rhodochrosite cabochons illustrating the banded pink colors that are characteristic of this mineral. The specimen in the upper right is a slice from a stalactite.
The primary ore of molybdenum and a minor ore of byproduct rhenium. Article by: Hobart M. King, Ph.D., RPG Molybdenite (gray) and quartz (white) in a specimen collected from the Henderson Mine near Empire, CO. Photograph by Scott Horvath, United States Geological Survey. What is Molybdenite? Molybdenite is a rare mineral composed of molybdenum and sulfur, with a chemical composition of MoS 2 .
A deep blue mineral, gem material, ornamental stone, ore of copper, and pigment. Article by: Hobart M. King, Ph.D., RPG Azurite with Malachite Nodule: A specimen of nodular azurite sawn and polished to reveal its beautiful blue structures. A specimen like this would be a superb gem material or ornamental stone.
Many were surprised when Canada suddenly became a world-leading producer of gem-quality diamonds. Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Diamond Mines: A map of Canadian diamond mines showing the approximate location of eight mines. Map by and MapResources. Table of Contents Diamonds in Canada?
A mineral used to make porcelain, as an abrasive, and occasionally as a gemstone Article by: Hobart M. King, Ph.D., RPG Blue kyanite crystals: A very common habit of kyanite is blue bladed crystals. Image by Aelwyn, Creative Commons license. What is Kyanite? Kyanite is a mineral found mainly in metamorphic rocks.
Most of Earth's crust is comprised of a small number of minerals. Article by: Hobart M. King, Ph.D., RPG The Most Abundant Minerals in Earth's Crust: Known as the "common rock-forming minerals", they are minerals present at the time of a rock's formation and are important minerals in determining the rock's identity.