I
cannot pretend to be partial about the colours, I rejoice with the brilliant ones…
Like Winston Churchill quoted above, I am quite
partial to bright colors found in some minerals, but this trait is likely
the norm among most collectors. And, I
am especially fond of green minerals—peridot, some garnets, some tourmaline, malachite,
emeralds, and several others. So, in perusing
my collection, I came across green examples of dioptase and diopside and
decided to further investigate. In fact,
I knew little about either mineral except several decades ago I attended a
summer geology field camp and was shown chrome diopside from diatreme rocks in
what is now the State Line Diamond District of Colorado and Wyoming. And, I
probably thought the two minerals were somehow related due to their color and
their “diop…”. However, I have found that
diopside is named for the Greek prefix di,
or two, while dioptase is for the Greek dio,
or through. And, they are not related.
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| BLOCKY, DARK GREEN DIOPTASE CRYSTALS FROM NAMIBIA. WIDTH ~1.0 CM. |
Dioptase is a hydrated copper silicate (CuSiO3-H2O)
whose emerald green color is due to the copper cation. The mineral is translucent to transparent,
the individual crystals are mostly six sided and capped by a rhombohedon. Although fairly soft at 5 on the Mohs scale,
some cutters facet the gemmy crystals but must install the finished stone in a
pendant—it is too fragile for a ring or bracelet.
 |
| NICE, SEMI-GEMMY CRYSTALS OF DIOPTASE FROM ALTYN-TYUBE, KAZAKHSTAN. WIDTH OF PHOTO ~4.0 CM. |
Dioptase is a secondary mineral that is found in
oxidized zones associated with hydrothermal replacement in copper sulfide
deposits. One specimen is my collection
came from the Christoph Mine, Kaokoveld Plateau, Kunene Region, Namibia. The best I can determine is that dioptase,
and several other oxidized secondary minerals, are found in limestones
associated with the Otavi Group (late Proterozoic [Precambrian] ~600-800 Ma). The mine, and adjacent area, is “famous” for
producing dioptase crystals.
 |
| MASS OF VUGGY, MOSTLY CERUSSITE, CRYSTALS FROM ARIZONA. SEE PHOTOMICROGRAPH BELOW. WIDTH ~ 2.1 CM. NICE, SEMI-GEMMY CRYSTALS OF DIOPTASE FROM ALTYN-TYUBE, KAZAKHSTAN. WIDTH OF PHOTO ~4.0 CM. |
The second specimen
is from the famed Mammoth-St. Anthony Mine (Tiger) located about 50 miles
northeast of Tucson in Pinal County. A
variety of metals, including gold, has been mined from the shafts but all
activity ceased many years ago. “Mineralization
in this district is a series of veins within shear zones…Their gangue consists
of brecciated country rock, cemented and replaced with quartz and calcite
together with some barite and fluorite” (www.mindat.com). My particular specimen is a mass of vuggy cerussite
crystals (clear and gemmy) with sparse tiny crystals of green dioptase, and
tiny arborescent “growths” of the mineral.
Very small partial crystals of wulfenite may also be present.
 |
| PHOTOMICROGRAPH OF GEMMY AND CLEAR CERUSSITE CRYSTALS WITH TINY GREEN CRYSTALS OF DIOPTASE. WIDTH OF PHOTO ~2.45 MM. |
Diopside may occur
in a variety of environments-- in hornfels associated with regional and contact
metamorphic zones, in kimberlites associated with diatremes, in metamorphic
gneiss and schist, and in skarns.
 |
| GEMMY CRYSTALS (PROBABLY CHROME-RICH) FROM MINAS GERAIS, BRAZIL WIDTH ABOUT 3.8 CM. |
I have two diopside
specimens, one from Minas Gerais, Brazil (Aracuai [Arrassuai], Jequitinhonha Valley)
where very gemmy crystals (probably chrome-rich) are associated with
quartz. The second specimen includes
several (some quite large), non-gemmy blocky crystals from the York River Skarn,
Hastings Co., Ontario.
 |
| LARGE DIOPSIDE CRYSTALS FROM HASTINGS. CO., ONTARIO. WIDTH OF TOP CRYSTAL ~2.4 CM. |
So, although
diopside and dioptase seem like they might be closely related, they are really “far
apart”. One is a hydrated secondary copper
mineral while the other is a magnesium-iron mineral usually found in
metamorphic rocks (or sometimes peridotites).
Churchill finished
by his thoughts about color by saying, and
I am genuinely sorry for the poor browns!
On Tuesday, November 16, 2021, 02:35:09 AM MST, Felicia Heath wrote:
ReplyDeleteI'm not sure of the resources used to explain Chrome Diopside, but I find it curious that you make no mention of the only place on Earth where chrome is actually found; Or that it was mined only three months of the year due to its lock under permafrost the majority of the year; Or it's hardness on the Mohs scale or specific gravity; Or that it is used in all types of jewelry in its natural unheated, untreated state because of the beauty of its spectral green color; Or that it hasn't been mined for a few years due to the mine owner's death, and that his heirs found the mining far too costly, given the low yield of gem-quality material. Lastly, your photos of Chrome Diopside don't resemble any rough I've ever seen. They may be of some form of Diopside, but not the one-source Siberian material that I collect.
Felica: I don't have the slightest idea of what you are talking about. Chrome ( only place on Earth where chrome is actually found;) is actually chromium and is found in several localities in 13 different countries--it is uncommon, Most chromium comes from the iron chrome oxide,chromite found in rocks around the world, at least in 17 countries.. Chrome diopside is not a mineral but simply diopside (Ca Mg silicate) with an enrichment of chromium. It is found in a large number of countries and certainly the gem variety comes from several countries and is a common variety. You can buy chrome gemmy diopside at a very reasonable price. It certainly is not a one-source gem. My photos of chromium-bearing diopside are pretty standard. And I stand by my resources. My suggestion---if you have some legitimate question, write me. But don't chew on my arse unless you know what you are talking about. I don't suggest that you contact me in the future, mike
Ha ha. Spot on mike
ReplyDeleteEverything I have read when I buy jewelry is that Siberia is where almost all chrome diopside comes from.
ReplyDeleteSure, most chrome diopside used in commercial jewelry comes from Yakutia and Siberia. It is not a really big jewel though since it gets cloudy and dark in anything over ~2 carats. And since diopside has two perfect cleavage planes stones can cleave and spall easily. And can scratch. A long time ago during my field camp we looked at a kimberlite in the WY-CO State Line District that had great chrome diopside. Think that pipe is off limits now to most collectors. The most fun later in life was looking for garnets and chrome diopside in ant hills in the green River Basin of WY. These minerals occur with diamonds in the kimberlites. No diamonds for me :( .
ReplyDelete