Azurite

Mineral Name: Azurite

Chemical Composition: Cu3(CO3)2(OH)2.

Color: Can be pale to dark blue, often with a little green.

Streak: Pale to dark blue

Hardness: 3.5-4, meaning it can scratch a penny but not glass.

Cleavage/Fracture: Cleavage plains are perfect at 011 degrees and poor at 100. This means there are two distinct cleavage points; this can be seen with one plain that is dull and another that glistens. The fracture pattern present in azurite is that of a conchoidal fracture. With this fracture pattern, the indentation is rounded, resembling a shell. (5,7)

Crystal Form: Azurite can have many crystal forms such as; tabular (which looks like a square tile that is 4-sided); prismatic (which looks like common quartz crystal and consists of 4 or more sides that have similar length elongated in one direction); equidimensional (which has all equal sides and looks like an uncut diamond), and earthy (this is be the most common form that crumbles when exposed to stress and has a dirt like hue). In addition, azurite is a pseudomorph, meaning that it has the ability to replace an existing mineral without affecting the external shape of said mineral. (1,2,3,4,5)

Luster: Vitreous, dull, adamantine

Special Features: When heated azurite is destroyed; it loses carbon dioxide and water turning into black, copper oxide powder. Also, this mineral is susceptible to hydrochloric acid, and as a result, it will fizzle. (1,2,3,4,7,8)

Varieties: Azure-malachite, which is a mix of both azurite and malachite, both copper carbonates. This variety will have a mottled green and blue coloring. (5)

Mineral Group: Azurite belongs to the carbonate group, which is a group whose minerals contain the chemical carbonate (CO3)2-. Carbonates are one of the most highly distributed minerals in the Earth’s crust and these minerals commonly occur with elements such as calcium, sodium, iron, or rare earth elements. There are currently 80 known carbonates and these minerals generally share characteristics like being soft or brittle and susceptible to hydrochloric acid. (9)

Environment: Azurite forms when groundwater enriched in carbon dioxide moves through the subsurface and comes in contact with copper ore. This water causes a reaction with copper ore, dissolving some of the ore which is then transported to a new area and deposited in an environment conducive to azurite formation. Azurite can also precipitate in void spaces and cavities in subsurface rock like limestone or sandstone. (5,6,7)

Associated Rock And Mineral types: Azurite is associated with sedimentary rock types such as dolostone, limestone, cherts, sandstone, siltstone, and shales. Linarite, lirconite, connellite, cyanotrichite, cornetite, and lazurite or lazulite are minerals associated with azurite. (10)

Occurrence in North America: The most common states geologist can find azurite is in Arizona, New Mexico, and Utah. (3,4)

Economic Uses: Azurite is often bought for it's deep blue color and, as such, is popular in jewelry or as a collector's piece. Unfortunately, azurite is difficult to use for jewelry because of its hardness on the Moh's hardness scale being only a 3.5 - 4. This hardness means that it can scratch a copper penny but not glass. The mineral is brittle and could easily break when set into a ring, necklace, or bracelet and does not age well when exposed to water or abrasion. Azurite can also be made into decorative items such as cabochons - minerals that are polished until they're smooth and the layers found in the mineral are clearly defined. (7)

When ground up into a fine powder, azurite can also be used for paint or pigment. This usage of azurite as a pigment was especially popular during the medieval period in Europe, with azurite mainly being used for paintings and makeup. However there were two major problems with the use of azurite pigment; one, that azurite is relatively hard to find and two, when azurite is exposed to light and air it slowly weathers into the green mineral malachite. As a result, azurite pigments were replaced with a stable man-made pigment called Prussian blue by the 18th century. (7)

Industrial Uses: Azurite was used as copper ore by early civilizations; but, because azurite is not wide-spread, it is now primarily used as a marker by industry geologist for copper ore. The bright color helps miners identify places where copper ore might be present, even if there is not an abundance of azurite. (7)

First Notable Identification: Azurite is thought to have been used by the ancient Egyptians first, as copper ore and pigment. However, the earliest written recorded to mention azurite is in Pliny the Elder’s Natural History. The original name for azurite was Lazhward, this was derived from the Persian word for blue and was later Latinized to aquarium. It was not until 1824 when mineralogist “ Francois Pendant” shortened the Latin word to what it is today. (8, 11)

How We Identified: Azurite has a dull earthy hue. The colors present are swamp green, black, and a Prussian blue. There are signs of fracture with the sparkles being quite notable and, when observed under a jewelers loop, the crystals appear to be sharp. The sample falls apart when handled, leaving a powder that is a Prussian blue along with a streak that is also Prussian blue.

Don’t Confuse It With: Some minerals you should not confuse with Azurite are linarite, which is softer, denser, and does not effervesce in hydrochloric acid. Another mineral that is similar is liroconite, which is slightly greener and less dense. Finally, lazurite is also similar but is found in the different mineral environment and is harder. The blue and green colors are the two main reasons as to why people have mistaken azurite in the past for other minerals, but there are multiple ways you can identify azurite instead of thinking it is one of these other minerals. (6,7)