Tag Archives: rock

Rapid City Gem & Mineral Show: Field Trips

The Western Dakota Gem & Mineral Society is gearing up for their 38th Annual Gem & Mineral show.  July 20th-22nd.  Details can be found here:  http://www.wdgms.org/2011Show.html

Field trips are being planned, and can be read about here:  Rapid City Field Trips

Trips include the Antelope Ridge, Black Hills National Forest & Hill City area, Railroad Butte / Farmingdale, and Conata.

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Hematite

[Guest Author Matt Doyle]

Hematite, famous modernly for the steel-grey jewelry often made from it, is more commonly a rust-red ore when found in mining iron[1].  A iron oxide (Fe2O3), hematite’s name comes from haema, the Greek word for blood[2], and most of its direct historical impact comes from that red form.  While hematite is incredibly common – the most common form of iron ore[3] – even in ancient times it was appreciated for itself, and not only for the metal it could produce.  In modern times, magnets are used to harvest hematite from mine tailings.

hematite1     Red hematite most commonly possesses an earthy luster, appearing anywhere from rust-colored to Powdered red hematite is also known as rouge.  Perhaps most famous as a cosmetic used for centuries to redden the skin, it is the same substance as jeweler’s rouge, used to polish metal and gemstones, and also frequently used to help strop a barber’s straight razor.  Red ochre and yellow ochre painting pigments also owe their color to a mixture of red hematite and clay – unhydrated in red ochre, and hydrated in yellow[4].  Maybe most strikingly, hematite is the basis of red chalk, and red chalk drawings have many prominent places in human history and the history of art, including the sketches of Leonardo DaVinci, the body painting of corpses in paleolithic cultures one hundred and sixty to eighty thousand years ago[5], and numerous cave paintings dating back as much as forty thousand years[6].  Red chalk mines dates back as far as 5000 BCE.

Grey hematite, unlike the “bloodstone” variety that gave it its name, has a metallic luster, and can appear almost like a dark mirror when sufficiently polished.  Faceted, it appears nearly black, and smooth, it has a gray, lustrous tone similar to a black pearl.  Used as a gemstone in jewelry, for gilding, or for carved intaglios, it was especially popular in Victorian England, and is still used today, in part because it is common enough to be relatively affordable. In its more jewel-like form, it has been sought after for over two millennia, since the Etruscans found deposits of it on the island of Elba.

hematite2     Outside of iron mines, hematite is commonly found in banded iron formations, hot springs, clay banks, and other places where iron interacts with water[7] (or more rarely, without water, as a result of volcanic activity).  Whether grey or red, it always leaves a red streak[8] (and a grey stone leaving a red streak is often striking and startling to students in the lab seeing it for the first time). Hematite often contains enough inclusions of magnetite to appear attracted to magnets, however, hematite itself is only weakly ferromagnetic when encountered at room temperature.  Its specific magnetic properties are variable in peculiar ways depending on the scale of the hematite crystal, and its small magnetic moment, as well as the temperatures at which it transitions from antiferromagnetic to paramagnetic, have been the subject of much discussion since the 1950s (and as such, could make up an essay – or many scholarly papers – of their own).

[1] https://en.wikipedia.org/wiki/Hematite

[2] http://www.mindat.org/min-1856.html

[3] http://geology.com/minerals/hematite.shtml

[4] http://www.mineralszone.com/minerals/ochre.html

[5] https://en.wikipedia.org/wiki/Pinnacle_Point

[6] http://www.eurekalert.org/pub_releases/2007-10/asu-rfe101207.php

[7] http://mars.nasa.gov/mer/spotlight/hematite01.html

[8] http://www.minerals.net/mineral/hematite.aspx

Rock Equipment For Sale

14″ rock cutting saw, 1 new blade, extra blade cutting oil
Polisher with stand & water drip pail
8 rock tumblers: 3-30lb capacity
Combination trim saw, grinder & shaper, sander & polisher
A lot of extra parts – some new, some used

New price would be over $5000, but I will sell all of this for $2500.

Contact

Melvin Berg
101 Stewart Ave, Box 736
Underwood, ND 58576

Grit – Treasures of Sea & Earth

Treasures of Sea & Earth supply grit for your rock tumbling needs.  For club discounts, please see the Member page.  For more information, please check out http://treasuresofseaandearth.com/ Currently available:

400                        5lb: $30.00         1lb: $6.00

600                        5lb: $30.00         1lb: $6.00

46/70                    5lb: $18.80        1lb: $4.00

120/220                5lb: $21.00        1lb: $4.20

Tin Oxide             5lb: $145.00     1lb: $29.00

Tripoli Powder   5lb: $18.80         1lb: $4.00

Plastic pellets     1lb: $4.20

Malachite

malachite3

Fibrous malachite

Malachite is an intense green colored, copper carbonate mineral. Instead of being a solid color, it is often banded in shades of green. While it can form tabular and twinned crystals, it is more often seen as botryoidal masses, or stalactitic, with a fibrous banded structure or crusts. Malachite can commonly be found with azurite. It has a hardness of 3.5-4 – soft enough to carve readily, yet still taking a polish. The stone is used for decoration, ornamentation, and jewelry. It can also be crushed and made into a green pigment. It was originally worn to ward off evil spirits.

Malachite comes from many locations, including Russia, Africa, Australia,

malachite2

Malachite with azurite

Brazil, and Arizona. It was named after the Greek word “mallows”, alluding to its leafy green color. It has also been called Atlas ore and Green Copper.

The chemical formula is: Cu2CO3(OH)2

 

http://www.minerals.net/mineral/malachite.aspx

http://www.mindat.org/min-2550.html

Pellant, Chris. Rocks and Minerals. New York: Dorling Kindersley, 1992. Print. Pg. 105.

Busbey, Arthur Bresnahan. Rocks & Fossils. Alexandria, VA: Time Life, 1996. Print. Pg. 174