Nestled in a gypsum formation in New Mexico, Pecos Diamonds are a strange variety of quartz. In addition to their unique shape, these “diamonds” come in a wide variety of different colors. They have several unique features that make them a favorite among rockhounds and a must-have for those who are primarily interested in quartz.
So, let’s dig to the heart of the matter and discuss Pecos Diamonds, what they are, and where to find them!
What Are Pecos Diamonds?
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Pecos Diamonds aren’t diamonds, despite the name. It’s one of the unfortunate things about letting people give stones names all willy-nilly, you end up with things like Herkimer “Diamonds”, Cape May “Diamonds”, and our subject at hand. All of these are quartz.
This variety of quartz is found in a wide variety of shapes, but most of them don’t really resemble the classic hexagonal, single-terminated shape that we generally associate with macrocrystalline silica. Instead, they show up in stranger geometric forms.
In addition to the rare crystallization forms, this strange quartz often takes on bold colors. The majority of these are red or yellow, but green, pink, and other shades can also be found. The sheer variety is a bit bewildering, especially if you’re only used to the “regular” types of quartz.
As a general rule, Pecos Diamonds are usually found as single crystals rather than clusters. That said, clusters do show up on occasion.
Strange Crystal Habits
The majority of these crystals are unique in that they’re double terminated. Double-terminated quartz occurs wherever quartz is found, but it’s generally very rare due to the conditions required for its formation.
Essentially, the quartz has to form inside the silica solution, which requires a vug (hollow place in the rock) with circulating water. Generally, quartz grows from the outside of the vug inwards, creating the normal variety of quartz points we’re all familiar with.
These double-terminated crystals have the potential to be elongated, although they’re rarer than stubbier crystals.
Another interesting crystal habit the quartz is found in is known as the Cumberland habit, sometimes called a Quartzoid habit. In this case, you have two hexagonal terminations without the normal prism faces between them.
Pseudocubic quartz is known in a few places, but it’s generally quite rare and generally very small. A high percentage of Pecos Diamonds fall into this habit, however, and they tend to be larger than other varieties. Pseudocubic quartz is actually a rhombus, but the angles are very close to the right angles required for a perfect cube.
Trigonal quartz is also found in this area. This form is similar to normal quartz, but the termination only has three planes instead of the normal six found in “standard” quartz. While quartz is considered to belong to the trigonal system, it generally falls into a hexagonal unit when it forms.
These are all rare varieties of quartz, but in the area where Pecos Diamonds are found they’re more common than almost anywhere else in the world.
Another strange tendency that’s found in these crystals is that a single piece may display different lusters on different faces. On other occasions, a very rough, knobby crystal may be found in a single piece with high-quality, well-formed quartz on the other end.
The Coloration of Pecos Diamonds
In addition to the unusual shapes that Pecos Diamonds are found in, they also come in a wide array of different colorations.
The only transparent crystals found in this area tend to be quite small. After a certain size, they have a tendency to take on the same coloration as the gypsum-rich sand that they come from. This tendency points to inclusions as the source of the color, rather than ions trapped in the crystal lattice like amethyst or citrine.
Indeed, sometimes they even take on the same “stripes” as the gypsum surrounding them.
Most of these quartz pieces are yellow to orange, with some red present. Milky white specimens with included gypsum are also found. Some are a deeper red color, and there’s also a variety that is a creamy olive shade of green. There are even black varieties found.
Where Are Pecos Diamonds Found?
Southeastern New Mexico is where these quartz pieces are found. The area where they’re found is rather specific, it’s known as the Seven Rivers Formation and it stretches over 100 miles and is roughly 25 miles wide at its largest point.
They don’t actually show up across this entire area, however. Instead, they’re found in specific outcroppings. Where they’re found, they’re rather easy to find even if you’re just surface picking. They can also be found along the banks of the Pecos River in most locations.
These outcroppings are scattered throughout the region, but as a general rule anywhere they’re present you’ll be able to find them on the surface.
Your best bet is to start with BLM land. Here you’re allowed to collect stones for personal use, including Pecos Diamonds. Other interesting minerals in the area include dolomite and aragonite crystals.
Don’t go on private land while you’re hunting. You’ll need to do your research to stay on the right side of the law when you’re exploring. If in doubt, check with a local to make sure that you’re not going to get busted for trespassing.
When you find an outcropping of these crystals, you’ll generally see glints of light on the ground, which is your indication that it’s time to start taking a closer look at the ground. They’re generally quite abundant once you’ve found a good spot.
A Word of Caution
New Mexico is a harsh environment, so you need to plan carefully. If you’re not acquainted with the desert, then you’ll want to avoid heading out in the summer. The area is incredibly harsh during summertime and it can easily overwhelm the unprepared.
You may also want to avoid hunting in the winter. While deserts are incredibly hot during the summer, they turn to bitter cold in the depths of winter. Fall or spring are your best bets, although spring often brings winds that can whip up the sand.
No matter what bring plenty of water for every person in your group. Double what you think you’ll need to bring if this is your first desert hunt. A first aid kit is also a good idea, especially if you’ll be far from your vehicle.
Keep your eyes open and avoid tall grass or tromping through bushes as well. There are eight species of rattlesnake native to New Mexico, and seven of them can be found in the Southeastern portion of the state that houses the Seven River Formation.
Common sense will keep you safe for the most part, the main mistakes people make is heading out when it’s too hot or not bringing enough water. Caution is advised, but it’s not a particularly dangerous area if you keep the above in mind.
How To Clean Your Pecos Diamonds
Because of the coarse sand that Pecos Diamonds are found in, they’ll often have exterior staining and bits of hard-to-remove dirt clinging to them. Some even have calcite on the exterior.If you want to see the true color, you’ll have to remove the stains and other debris that are on the surface.
The best way to proceed is by beginning with warm soapy water. This isn’t capable of damaging the stone in any way and will remove everything loose on the stone. If the surface is pitted, then a toothbrush will let you get debris out of the cracks, pits, and other surface imperfections of the crystal.
If you’re still having trouble getting them clean, try using a solution of white vinegar and water in a 1:1 ratio. Soak the stones for an hour or so and then scrub them with a brass wire brush. Steel will work as well and shouldn’t scratch the stone but I generally prefer brass as it’s the softer metal. This will remove the rest of the stains and any calcite clinging to the surface.
Since the coloration of the stones comes from inclusions, rather than being the effect of something like hematite clinging to the surface, this won’t affect the coloration of the stone and will instead let you bring out the true colors so you can enjoy them.
Pecos Diamonds
Classification: Variety of quartz
Chemical Composition: SiO₂ (silicon dioxide)
Color: Typically clear or translucent with hues of red, yellow, or brown, often containing speckles or inclusions that add to their uniqueness.
Streak: White
Hardness: 7 on the Mohs scale
Cleavage: None
Fracture: Conchoidal
Luster: Vitreous to waxy
Transparency: Transparent to translucent
Crystal System: Hexagonal
Formation and Geology: Pecos diamonds are not true diamonds but rather quartz crystals that naturally form double terminations and are found in the gypsum and dolomite-rich soils of southeastern New Mexico, particularly around the Pecos River area. These quartz crystals grow in a unique sedimentary environment, where they crystallize in the spaces within or between rock layers. The presence of various trace minerals contributes to their coloration and patterning.
Physical Properties: Pecos diamonds are known for their crystal clarity and the double-terminated points that they frequently exhibit. These characteristics make them particularly appealing to collectors. The varied colors and inclusions within the crystals are due to impurities and the particular conditions of the surrounding soil and rock.
Identification Tips:
- Color and Clarity: Look for the unique speckled coloration and clear to translucent quality.
- Crystal Form: Double-terminated crystals are a distinguishing feature of Pecos diamonds.
- Hardness: Being quartz, they can scratch glass and metals softer than 7 on the Mohs scale.
- Texture and Luster: They typically have a vitreous to waxy luster and a smooth texture.
Locations: These crystals are primarily found in the area around the Pecos River in southeastern New Mexico. Specific notable locations include areas near Roswell and Artesia, where they are scattered across the desert floor and embedded in soft rock formations.
Uses and Significance: While they have no significant commercial value, Pecos diamonds are highly valued by mineral collectors due to their unique beauty and the peculiarities of their formation. They are also of interest to geologists and educators for demonstrating the diverse forms that quartz can take and the environmental conditions that affect mineral formation.
