Physical aspects and appearance Turquoise is a mineral known first and foremost for its color--the color turquoise is, in fact, named after the mineral. In mineralogy, color is usually highly variable and is rarely reliable as a diagnostic trait, but that is not so with turquoise. Though the blue-green coloration is not unique to turquoise, the color is so intrinsic to turquoise that it will be an identifying feature when distinguishing it from most other minerals. That is because turquoise''s trademark color is idiochromatic , which means that its color is derived from its essential elements--namely copper--as opposed to many other minerals whose color is often determined by impurities of other elements and minerals trapped in their internal structure. But turquoise''s color is not without variation: Some turquoise is more deeply colored while others are more pale, some are vividly blue, and others will be much more green in hue (a trait caused by the addition of iron to its composition). Coloration can certainly vary greatly from one turquoise deposit to the next, but it can even vary within individual deposits. Turquoise very rarely forms crystals and instead is almost always found massively . These solid growths consist of tiny intergrown grains of turquoise; the more tightly bonded to each other they are, the higher quality and more colorful the resultant turquoise specimen tends to be.

But between the tiny grains are even tinier voids; these pores can become filled with other minerals or substances that can change the physical characteristics of the turquoise. Some specimens with larger pores will have poorer coloration and appear to be softer and more fragile due to lessened cohesion between grains. More porous turquoise also allows more weathering agents--particularly water--to soak into and weaken the turquoise, leaving it chalky and crumbly. The variability of the cohesion of turquoise grains can also affect the mineral''s trademark color. Turquoise is prone to fading or changing color over time, especially with continued exposure to light and moisture. Porous, low-grade turquoise may appear in vivid shades of blue when mined but often fades to grayer hues shortly after extraction. Conversely, better quality, denser turquoise will retain its vivid coloration much longer. All turquoise, however, weathers relatively quickly when left in the elements, developing a chalky white husk, eventually turning an entire vein or mass of turquoise to clay.

Turquoise masses are usually irregular in shape and fill cavities or cracks in rock, formed there long after the rock itself. As such, the host rock can vary greatly in type and composition. In many cases, the host rock shares nothing of turquoise''s color or traits, causing the turquoise veins to contrast vividly in color, making for very apparent and attractive specimens. Turquoise with even, consistent coloration and no impurities is often considered to be the best and most valuable. But most turquoise contains subtle variations in color and small imperfections, usually inclusions of other minerals or its host rock embedded within it. These veins and masses of other materials are referred to as matrix , a term for the other materials with which turquoise is found embedded and intergrown. A desirable kind of inclusion is known as a "spiderweb" pattern, or "spiderwebbing," which appears as a network of intertwined veinlets of dark mineral inclusions. Sometimes the spiderwebbing is slight, creating lace-like patterns, but it can also be extensive, with broader "webs" or "nets" appearing to fragment the turquoise, dividing the blue into small cells of color.

The finest, best-formed turquoise is that which is solid enough to be cut and polished, while the lowest grade turquoise is usually chalky, crumbly, and nearly impossible to polish without disintegrating. Turquoise is moderately hard when finely formed, usually able to be scratched by a steel knife or piece of glass but not by a copper or nickel coin. Less cohesive, grainier specimens may seem to be softer, and the chalkiest specimens will appear to be scratched with just a fingernail; this is indicative not of a softer type of turquoise but of the turquoise grains being less compact and more loosely adhered together. Conversely, turquoise that has been naturally indurated , or made harder by other mineral solutions such as silica (quartz), will have a higher hardness. In nearly all cases, turquoise is opaque, with only very thinly cut or broken pieces showing any amount of translucency. It is also a very brittle mineral, easily broken when struck or dropped. Before polishing, the very finest turquoise will have a luster similar to wax (its surface will reflect light in a manner similar to wax), but the majority of specimens will have a dull luster. After being polished, turquoise will appear much shinier but won''t be as reflective as glass unless it has been naturally indurated or artificially treated.

Chemically, turquoise is a copper-bearing hydrated alkaline aluminum phosphate. Phosphate minerals contain the element phosphorus chemically bonded to oxygen as an essential component, often then bonding with a metal--aluminum is common--and, in the case of turquoise, hydroxide (alkaline) molecules and water. But turquoise also contains some copper atoms bonded to oxygen alongside the aluminum, which gives turquoise its namesake color. It''s this copper content that gives turquoise its "identity" and distinguishes it from other closely related minerals.