Whether they will admit it or not, most placer miners have voiced unkind comments about magnetite. And that’s understandable because magnetite is the primary component of the ubiquitous, heavy, black sands that often clog sluice box riffles. But there’s another side to magnetite that deserves respect, for this iron-oxide mineral has profoundly influenced history, culture, industry, and science.
The best-known variety of magnetite is lodestone. Its natural magnetism has created colorful alchemistic lore; greatly advanced navigation, surveying, and cartography; and inspired landmark breakthroughs in scientific thought. Magnetite made possible the early voice recorders that revolutionized radio broadcasting; today, it is used in many industrial dense-media-separation processes.
And that’s not all. More than a half-billion tons of magnetite ore are currently mined worldwide each year as a source of iron. And geophysicists study magnetite grains in igneous rocks to learn about the ancient Earth’s magnetic fields and tectonic-plate movements.
Magnetite (iron oxide, Fe 3 O4 ) consists by weight of 72.36 percent iron and 27.64 percent oxygen. It crystallizes in the isometric system, usually as octahedrons, occasionally as dodecahedrons, and rarely as cubes. Opaque and with a submetallic-to-metallic luster, magnetite is black to dark-gray in color with an occasional hint of blue iridescence. Brittle and with a subconchoidal-to-uneven fracture, it has a Mohs hardness of 5.5-6.5 and a substantial specific gravity of 5.17.
この記事は Rock&Gem Magazine の July 2021 版に掲載されています。
7 日間の Magzter GOLD 無料トライアルを開始して、何千もの厳選されたプレミアム ストーリー、9,000 以上の雑誌や新聞にアクセスしてください。
すでに購読者です ? サインイン
この記事は Rock&Gem Magazine の July 2021 版に掲載されています。
7 日間の Magzter GOLD 無料トライアルを開始して、何千もの厳選されたプレミアム ストーリー、9,000 以上の雑誌や新聞にアクセスしてください。
すでに購読者です? サインイン
Rockhounding Ohio's Lake Erie Islands
A short ferry boat ride three miles from Ohio’s Lake Erie coastline is South Bass Island, better known as Put-in-Bay or the “Key West of the North.”
Iowa's Hidden Treasures
Exploring Keokuk Geodes: How They're Made & What's Inside
Agatized CORAL
Florida's Collectible State Stone
Rockhounding Florida's Beaches
Beachcombing serene stretches of Florida can reveal fascinating finds like fossilized shark teeth, sea glass, quartz, agate and even coral fragments.
Collecting Staurolite
Hot Spots In Virginia & Georgia
Pecos Valley Diamonds
New Mexico's Ancient Attraction
12 Tips for Rockhounding Tucson's Greatest Shows
Tucson in February becomes the international hub for buying and selling colored gems, rocks, minerals and fossils.
Turquoise in the American Southwest
A Water & Sky Souvenir
Touring Colorado's MINERAL BELT
It's a Showcase of Mining History & Minerals
Geology &Colorado's Taurish Traiks
Most of Colorado’s tourist trains today were originally constructed in the late 1800s to serve the state’s lucrative mining operations.