Colorado Gem & Mineral Co. - Rocks for the Rest of Us

Rock Talk and Information from a Geologist


Welcome to the informational section of our website!  Hopefully you'll find out something you needed to know.

DEFINITIONS

Euhedral : having sharp, recognizable crystal faces
Anhedral : lacking clear, recognizable crystal faces
Subhedral : an intermediate texture, displaying partial crystal face formation
Alluvial : found in loose sediments (alluvium) , typically eroded by water
Epitaxial : exhibiting orientation inherited from a host mineral (attaching minerals will show an alignment)
Botryoidal : having an external form composed of round segments, reminescent of grapes
Vug : a small to medium sized cavity in rock, typically lined with crystals
Floater : a crystal formed without signs of contact to the host rock, "floating" in suspension
Flower : marketing term given to crystal groups resembling flowers, typically those with outward facing crystals reminescent of petals
MINERAL INFO

 Thumbnails and Toenail Collections  An excellent system for mineral collectors is to build a systemic collection (the various crystal systems, ore minerals, a single mineral, silicates, oxides and sulfides, gem minerals, etc. are possible themes.)   Once you decide on your systemic collection theme, you can stick to similar sizes for the specimens, and going small is excellent for two reasons:  Takes up limited space, and small sizes are less expensive and more available. 

Two sizes that are popular are Thumbnails and “Toenails.”  Thumbnails fit inside a 1” cube.  “Toenails” are that size that is a little too big for a thumbnail and therefore is often cheaper than if it were the size of a Thumbnail.  Miniature specimens are those that fit in a 2 inch cube but larger than 1 inch cubes, so miniatures include “toenails.” Cabinet size refers to any specimen larger than 2 inches. Large Cabinet size us usually understood to be over 4 inches.  Remember one inch is 2.54cm.  A handy reminder is 5cm =2 inches. Remember the rule that Nature makes crystals in small sizes more perfect than larger ones. Remember the rule that Nature makes crystals in small sizes more perfect than larger ones.

 

When you are buying a new specimen for collection the specimen should be: Well-formed single crystals or groups free of crusts, blemishes, dings, cracks, or anything that distracts from the aesthetics.  Coatings of other minerals sometimes can be removed mechanically or chemically by experts. Many collectors prefer some matrix or “mother rock” for the feature crystals to show the natural environment they were found in.

-Without damage that is very apparent and distracts from appearance while on display. The main crystals be intact and hopefully not repaired back to the matrix. Glue usually fluoresces and material is missing if closely examined.  It happens in all countries of origin and with owners who may or may not have repaired them.  Beware of mixtures of ground up material oddly placed only around base of reconnected crystals.

-Look for color- a good collection will have most colors of the spectrum.

-If it is a matrix specimen it sometimes can be trimmed with a mechanical trimmer or diamond saw.  Experts know how to make the saw cut rough looking after strategic cuts. Fragile specimens can be mounted on a small Plexiglas base using “mineral tack” which is a non oil sticky clay like silly putty but it can be easily removed after long periods of time without leaving residue.  A base also can position a specimen to be in the best display angle.  If a specimen displays well without a base, all the better. Resist letting others handle your specimens unless you know them to be the right kind of person who is careful with rare collectibles.  And always handle over a soft surface in case you drop it.

Mineral specimens for collections don’t need to be like the famous museum caliber specimens often pictured in books and trade literature.  Check prices on the internet mineral websites and Ebay.  Go to shows and join mineral clubs. Ask dealers on websites if they have other specimens, they often will have similar specimens in different sizes, depending on what they are known to sell.

-If you want to give a small new collection to a young person, let us know and we can put together any size collection at very reasonable price.  We have lots of surplus minerals from 50 years in business, and encourage new collectors.

 

 


Zunyite : The salt dome near the village of Qalat-e-Payeen is situated 24 km NW of the harbor of Bandar Abbas. It was also known as Qalat-e Bala in Bosák et al. (1998). The highly deformed and concentrically structured plug, 4 km in diameter, is composed of numerous hills of light colored (whitish, yellowish, pink, greenish) rhyolite to rhyodacite with porphyritic texture, tuffs (ash, sandy and lapilli-bearing varieties) and ignimbrite. They are heavily altered and highly fractured and contain fluorapatite, fluorite, hematite, zunyite and cubes and pyritohedrons of limonite after pyrite. There are also green metamorphics with epidotized and hematitized fractures. Purple to brown shales to siltstones are only sometimes inter-bedded with sandstones. A few meters of light to dark gray carbonate beds (limestone, dolomitic limestone and dolostone) are also exposed.

Demantoid, var of Andradite Garnet : The rare gemstone variety of Andradite is rarely found in large crystals.  Iran has two localities, Sogham has more gemmy material, while new production from Belqeys Mtn Belqeys Mountain (also Bolgheis Mountain)  is probably going to be the world premier locality for specimens.   It is located 34 km NE of Takab  36° 40' 6'' North , 47° 17' 53'' East 34 km NE of Takab West Azerbajian Prov. M79X+86 Gharavolkhane, Zanjan Province, Iran Bolgheis Mountain, Iran

Rainbow or Iridescent Quartz : In 1950 Dr. C.V. Raman (father of Raman Spectroscopy) published the discovery of a colorless Quartz that exhibits adularescence, or iridescence. It occurs in druse veins emplaced in basalts, and it has also been discovered in Argentina on the slopes of a volcano. Jack has found a good source for very fine specimens from India, and we now offer them on this website. We call it Rainbow Quartz; the locality is Madhya Pradesh, India.

It is difficult to capture all the colors that a specimen displays in a photo. Rest assured that these specimens will show neon color in nearly all the crystals on a specimen, changing as the specimen is viewed from different angles. The colors are due to polysynthetic twinning in the crystal; and this is not the same as interference pattern rainbows seen in fractures of clear quartz. The cause of this structure in basalt related quartz has not been determined.Amethyst discovered by Jack Lowell in Uruguayan Basalts exhibits this optical phenomenon and is named Lowell Effect Amethyst by the Gemological Institute of America.

Alaska gold is almost never found in crystal form; nuggets are the order of the day, and have been since the Alaska Gold Rush of 1898. The largest gold nugget ever found in Alaska is named the "Alaska Centennial Nugget." It weighs a whopping 294.1 ounces (20.1 pounds) troy, and was found in 1998 --- the 100th anniversary of the Gold Rush --- along Swift Creek near the town of Ruby, Alaska by Barry Clay (he turned it up with a bulldozer!). It's the second largest nugget ever found in the Western Hemisphere, number one being the "Boot of Cortez" found in Mexico. The second largest from Alaska is the "Anvil Nugget" (182 ounces), found along Anvil Creek near Nome in 1903. Plenty of other big ones have been found as well. Number 20 on the list is the "Silverado Nugget" (42 ounces), sold to a collector in Spain in 2000 for $50,000. For a look at more Alaska nuggets see the website of AKMining at http://www.akmining.biz/mine/nuggets.html

Faden Quartz : Faden Quartz starts as grains of quartz in a rock split by earthquakes, and become intricate and beautiful patterns trying to bridge an ever widening fissure deep in the earth.

These represent a very unique geologic phenomena that occurs when certain minerals (apatite, quartz, et al.) grow in a fault zone, as movement continues, here quartz deposition continues to add to a chain of quartz that has deformed and yet fully terminated and brilliant crystals that mend, knit, and augment the broken chain as the earth movements persist.

When uncovered by erosion and mining, these minerals are found in amazing chains, or floater singular compound crystals with nearly unrecognizable habit.

Chrysanthemum Stones : Most of the Chrysanthemum Stones in China are from Hubei Province, and there are many "embellished" C. Stones from Hunan Province, they occur in a grayish limestone and the patterns are very faint irregular shapes with edges similar to what pinking shears do to cloth, a zig zagging pattern.  The material is darkened by putting black color on the whole rock after outlining the pattern in pencil.  Then the design is painted on with white paint.  Immersing these in water will show a loss of contrast between the rock and design. Genuine Chrysanthemum Stones (Hubei Province) have patterns made of solid calcite/strontianite/quartz mixture shapes, often petal shaped, and often resembling flowers.  Recurrent themes are "Palm trees" and "fireworks."  There have been huge assembled stones up to four feet tall, they have been manufactured by placing real patterned stones together in a synthetic black medium that is very close to the carbonaceous limestone of the genuine stones. The collecting areas are currently being covered by a new reservoir and the stones will become very rare now. There are also some rare ornamental stones from Igneous rock in Japan that are fashioned into beautiful presentations with small polished tablets of the rock with custom bases with graceful design. These are called Suiseki.

We sent a Chrysanthemum Stone from Hubei Province, China to Bob Downs at the Univ. of AZ and the white material is a mixture of Strontianite and Calcite.  Almost all the literature says Celestine instead of Strontianite.  Most of the Chrysanthemum Stones in China are from Hubei Province, and there are many "embellished" C. Stones from Hunan Province, they occur in a grayish limestone and the patterns are very faint irregular shapes with edges similar to what pinking shears do to cloth, a zig zagging pattern. The collecting areas are currently being covered by a new reservoir and the stones will become very rare now.

Our lab results indicated the flower stone is composed of : 83% Strontianite, 10% Quartz and 7% Calcite.

 

Care of Pyrite and Quartz Specimens

Pyrite, especially the sharp edged cubes from Spain and other localities, is very easy to chip if touched to a hard surface..  It is relatively hard but brittle.  To shine up a Pyrite specimen, plain old toothpaste and a toothbrush are fine.  After it is rinsed, it is good to rinse in baking soda water, and then spray with rubbing alcohol to avoid water spots when dry.

Quartz is also very brittle, and the value of a good specimen is partly in it’s condition, ie, lack of damage including chips esp. on the tips of crystals.  To clean Quartz, ammonia with water and a bristle brush are good.  After it’s cleaned up, rinse with distilled water, or tap water and then follow with a spray of rubbing alcohol to prevent water spots. Make sure not to hit the specimen on any hard surface., or contact it with other quartz.

 

Here is a common question we receive.   "How can a euhedral, clear Quartz crystal sit on what seems to be cement as matrix?"

The explanation really is that down in the ground formations tend to crack and move.  And rock is ground into grains and pebbles, called Breccia when it is larger than a pea and sometimes a gossan, which is rock that has been smeared into a clay.;    In a quartzite/ limestone strata like the one in Payson, AZ through time the quartzite exposed by movement in the ground and later fluids carrying dissolved silica got in between those little grains of sand that originally formed the Quartzite, altering them into a rough sandpaper like rock at the surface and the larger grains are still there, in the meantime crystals forming upstream get washed through the cracks and end up getting set onto a  horizontal area and get attached with silica while growing larger in place.  Quartz can grow surprisingly close to the surface in geologic time.   What forms the quartz is the fluids that migrate up and down through the strata. Think of  quartz crystals starting with some grain or "seed" down in the depths.  


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