Malachite

Malachite, the most distinctive of the green minerals, has had a long reputation for protection. As long ago as 4,000 BC, malachite was mined in the Sinai Peninsula, and ancient Egyptians ground malachite on sacred palettes to make Udju, an eye makeup that was believed to bring protection from the goddess Hathor. Sinai and its mines were under the dominion of Hathor (the goddess of beauty, joy, love, and women), who was also known as the "Lady of Malachite."

Archaeologists have found evidence that kits for grinding malachite eyepaint were a very important item in the Egyptians' toilette. Interestingly, the Egyptian word for these kits is quite similar to the Egyptian phrase "to protect." Wearing Udju was practical in reducing the glare of the sun (much as football players wear grease paint), and was believed to guard against the evil eye. However, it's unlikely that the ancient Egyptian women realized that the metallic ions of malachite (an oxide of copper) made an extremely efficient antibacterial agent, protecting them from all types of infection. Infections of the eyes were common due to flies and flying sand, and wearing malachite likely reduced them.

However, long-term use of Udju couldn't have been healthy -- the high copper content of malachite (57%) makes it toxic. This makes it dangerous to mine, cut, or hand-polish malachite without proper protective equipment. Luckily, it's completely safe to handle rough and polished specimens.

Malachite is a secondary mineral of copper, which means it's formed when copper minerals are altered by other minerals. It occurs when carbonated water interacts with copper minerals, or when a solution of copper interacts with limestone. Malachite forms relatively quickly -- bronze objects have been found at ancient Assyrian sites partially or wholly converted into malachite! The green patina on weathered copper roofs and statues is a form of malachite. Because of its presence in nearly all oxidized copper deposits, malachite serves as a prospecting guide for (and an important ore of) copper, and is found in small quantities all over the world.

The distinctive banding is caused by subtle changes in the oxidation states of the surrounding pore waters, but the exact mechanism is still not well understood. Though the massive form is the most well-known, having been used for carved figures and household decorations for centuries, a less common but spectacular form is fine acicular hairs that group together to form a carpet of green "velvet," as shown here.

Malachite: Cu2(CO3)(OH)2, Copper Carbonate Hydroxide
Habit: massive forms are botryoidal, stalactitic, or globular; crystals are acicular or fibrous and form in tufts and encrustations
Hardness: 3.5-4
Luster: massive forms are dull; crystals are silky
Transparency: massive forms are opaque; crystals can be translucent
Cleavage: perfect, but rarely seen
Fracture: conchoidal to splintery
Specific gravity: 3.9+ (noticeably heavy)
Streak: green
Other: weakly effervesces in acid

About Tumbling Grit

Abrasives used in the art of tumbling come in a wide range of grits, and in a lot of different materials. This can be confusing to the newcomer. Here are some of the terms you'll need to know:

Grit refers to the size of the particles, and as with sandpaper, the smaller the number, the larger the particles are. 60/90 –- which means a range of particle sizes between 60 and 90 grit -- is the coarsest grit generally used in tumbling, though 46/70 is available. 500F or 600F is generally used for the prepolish step, although some people use 800F or even finer for prepolish. (The "F" means "and finer".)

Mesh is a little more precise, referring to the screen through which a particular grit must pass. The term mesh is more commonly used for abrasive sizes 1000 and higher. For practical purposes, however, grit and mesh can be considered the same thing: 1000 grit = 1000 mesh.

A micron is 1/1000 of a millimeter. About the only time you'll come across this measurement is with certain polishes, like Linde A and Linde B. In the case of microns, the larger the number, the larger the particles -- the inverse of how the terms grit and mesh work. Therefore, 120 grit equals about 100 microns, whereas 220 grit equals 70 microns and 600 grit equals 25 microns.

Silicon carbide is the basic abrasive used in tumbling. It is very hard –- Mohs 9+ -- and each time it breaks, a new sharp edge is exposed. This makes it long-lasting and quite effective.

To learn about more types of tumbling grit, read the rest of this article online.

In addition to our pre-packaged 4-Step Grit Kit, we now offer individual 1-pound bags of 47/60, 80, 220, 500F, 800F, and CPP Polish, as well as burnishing media, online. In July, we'll be adding Red Rouge, Cerium Oxide, Chrome Oxide, Pro-Polish, and Walnut Shell!

How to Pan for Gold

Panning for gold can be a lucrative hobby -- or a great family activity. It's a relaxing (or exciting!) way to spend some time outside and get in touch with nature. To be really successful, perseverance and patience are necessary, but the thrill of finding even the tiniest flake of gold is worth the effort!

First, a word on why gold panning works:
 
Gold commonly occurs with other minerals that, like gold, are heavier than quartz (which makes up the majority of the silt and sand in a stream bed). Quartz has a specific gravity of 2.65, which means that its weight is 2.65 times an equal volume of water. Black-sand materials have specific gravities ranging from 3.4 to 5.5. Gold has a specific gravity which, depending on its silver content, ranges from 15.6 to 19.3, which is why it occurs at or near the base of the riverbed sand deposits and why it migrates quickly to the bottom of the gold pan.

1. Find a good set of gold pans. Look for ones with riffles around the edges, since these help the gold to separate from other particles more easily. A classifier pan is useful to remove the larger gravel from your panning material (make sure you don't throw out any nuggets!). Green plastic pans work better than metal pans because they are lighter, have shallower angles (which reduces the risk of losing some of your gold), and because gold is easier to spot against the green background. We carry two affordable Garrett gold panning kits that will provide you with everything you need to start your gold-hunting adventure.
    
   
2. Find out the recreational prospecting regulations of the area before you begin. Regulations vary by state, but Placer Gold Deposits books are a good place to start (if available), and the Bureau of Land Management and your state's Department of Natural Resources should have information on existing claims. LEARN MORE about where to find gold in the U.S., or check out our great selection of prospecting books for more information.
    
   
3. Choose a location along a river or creek, preferably one where the bedrock is exposed or not heavily covered by clay and soil. Places where the water slows down noticeably, such as behind sandbars or boulders, are usually good spots for panning. After a heavy rain, choose a location farther downstream -- much of the gold will have been washed away from its source by the current.
    
   
4. Sit your classifier pan inside your large gold pan and fill it almost to the top with sand from the edge of the creek or river. Use your hand shovel -- deeper is generally better. Gold will usually be concentrated in the bottom 6-8 inches of sand and gravel above bedrock. When your pans are full, lift the classifier pan out, shaking it gently, to remove the gravel. Check for nuggets before you discard!
    
   
5. Dip the pan's edge into the stream and fill it with water. Use your fingers to mix the sand thoroughly with the water, to create a slurry.
    
   
6. Hold the pan with one hand and swirl or shake it back and forth to mix the sand. Any gold will start settling toward the bottom of the pan.
    
   
7. Swirl the pan faster. You will lose some of the water, along with lighter particles of sand, as you go. The more you swirl, the more the heavier materials will settle to the bottom of the pan, where you'll find the gold. Add a little more water to keep everything moving smoothly -- this also helps the gold settle.
    
   
8. Scrape the top layer of sand out of the pan with your free hand, or tilt the pan and let the top layer fall away. Always keep the bottom of the pan lower than the lip. You will eventually get down to a layer of black sand (as a general rule, if you don't have any black sand, there won't be any gold). One of the components of this black sand is magnetite, which is difficult to separate from gold, but a good sign that you'll find something!
    
   
9. At this point, you may want to carefully transfer your remaining material to a smaller finishing pan (this makes it easier to find the flakes of gold you may miss in the larger one). Tilt the pan at a 30% angle and swirl the pan, imitating the motion of a spinning coin just before it comes to a stop. As you move it more quickly, the gold will lag behind the other material in the pan, because of its greater specific gravity.
    
   
10. Pick out larger gold samples with your fingers and use tweezers or a suction bottle for tiny particles. Put your finds in a small vial, and show them off to your friends and neighbors!

How to tell if what you've found is gold (and not fool's gold):

• Try using a straight pin to stab the specimen. Gold is a very soft metal and will bend or break when you do this; iron pyrite is much harder and won't budge.
• Take a magnet with you. Iron pyrite will stick to the magnet because of its high iron content; gold will not.
• Rub the nugget across an unglazed porcelain tile. Iron pyrite will streak black, while gold's streak is gold.
• If you have a 10x magnifier (or loupe), examine your find closely. Pyrite has a cubic structure; gold does not.

Fun idea:
 
For your next kid's (or grownup's) birthday, have a gold panning party! All you need is a few gold pans, a plastic kiddie pool full of sand and gravel, and some pure gold pieces and/or pyrite to "seed" the sand. Imagine the excitement when your child (or rockhound spouse) finds the Mother Lode! The traditional exclamation of success is "Bonanza!"

Geology Word Puzzler

What terms are used by geologists to describe the appearance of a mineral, and what do they mean?

Luster: (LUS-tur) the appearance of a mineral in reflected light. A mineral is often labeled with more than one descriptive term, and lusters may be combined (e.g., adamantine-metallic, resinous-greasy) for minerals that don't fit clearly into one category.

metallic (having the brilliant appearance of metal) -- pyrite, hematite (polished)
vitreous (having the luster of glass) -- quartz
resinous (appearing like resin) -- smithsonite, amber
pearly (having the iridescent appearance of a pearl) -- lepidolite
greasy (appearing to be covered with a thin layer of oil) -- talc
silky (looking like silk) -- serpentine
adamantine (having a hard brilliant luster) -- diamond
waxy (having the appearance of wax) -- turquoise
earthy (looking like dirt or dried mud) -- hematite (rough)
fibrous (appearing to have fibers) -- malachite
dull (having a non-reflective surface) -- tektite, goethite

We'd love to hear from you! Have questions or comments about the website, or just want to tell us about your latest rockhounding adventure? Email us at we_rock@mamasminerals.com!

Read about rose quartz, geodes, and identification of rocks and minerals in the Fall 2006 issue of RockZ NewZ

Read about rose quartz, geodes, and identification of rocks and minerals in the Summer 2006 issue of RockZ NewZ

Read about fluorite, fluorescent minerals, and cleaning quartz in the Summer 2005 issue of RockZ NewZ.

Read about vanadinite, building fountains, and identifying meteorites in the Winter 2004 issue of RockZ NewZ.

Read about celestite, pearls, and how to choose the right rock tumbler in the Fall 2004 issue of RockZ NewZ.

Read about amethyst, fossil preparation, and field tools for the rockhound in the Spring 2004 issue of RockZ NewZ.

Read about galena, petrified wood, and collecting micrometeorites in the Winter 2003 issue of RockZ NewZ.

Read about iron pyrite, tumbling seaglass, and stony meteorites in the Summer 2003 issue of RockZ NewZ.

Sign up to get each new issue delivered to your inbox!