Tyrolite with Azurite (#68)

Bright lustrous turquoise lathes of tyrolite to ¼" in mats on and with lustrous micro crystals and masses of azurite.
North America Centennial Eureke Mine, Tintic District, Juab County, Utah 1 ¾" x 1 ½" x 1"

 

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The blue mineral in this specimen is azurite, and there are so many specimens of, or including, azurite in this display that there is little left to write about it. Tyrolite is the green mineral. It is another of the secondary minerals found in oxidized zones of ore deposits (see Learn More for specimen #30), and has the chemical formula Ca2Cu9(AsO4)4(CO3)(OH)8 • 11H2O. The symbol As is for arsenic. So this might be classified as an arsenate. CO3 is the carbonate group, so it might be classified as a carbonate. Most formal classification systems (of which there are several) identify tyrolite as an arsenate first, and within a subgroup that contains the carbonate group.

One might wonder why it is important to classify minerals in the first place, and if it is, why not just classify them by color, since that is generally the first characteristic we notice. The answer is that classification schemes, while often tedious to design and sometimes complex, tell us much about a mineral and may lead us to significant questions. A classification scheme answers the question, what? From there we can pose questions about why.

A classification scheme based on color, for example, might be useful as a step in simply identifying minerals, but it would tell us nothing of their chemistry or crystal structure, which are scientifically more significant than color. We use, primarily, a scheme based on chemistry (silicates, carbonates, sulfides, etc.), and for some large and structurally diverse chemical families, like silicates, another classification scheme based on aspects of the crystal structure is employed.