Axinite is a distinctive group of brown to violet minerals composed of calcium aluminum boro-silicate. Known for its sharp, bladed crystals, it is both piezoelectric and pyroelectric. The group includes iron, magnesium, and manganese-rich varieties, each with their own specific color range.

Aventurine is a translucent quartzite known for its glittery "aventurescence," caused by platy mineral inclusions. Green, from fuchsite mica, is most common, though it also occurs in orange, brown, and blue. As a rock, its hardness and density can vary slightly.

Apatite is a group of phosphate minerals (fluor-, chloro-, and hydroxy-) often mistaken for other gems, a deception referenced in its Greek name. It is the source of the phosphorus in fertilizer and, as hydroxyapatite, is the main component of vertebrate bones and teeth.

Andesine-Labradorite is a crystalline gemstone blending two feldspar minerals. Its name honors their discovery locations: the Andes Mountains and Labrador, Canada. The hyphen denotes its chemical composition, which falls precisely between pure andesine and labradorite, resulting in its unique and descriptive classification.

Ametrine is a rare quartz variety featuring striking purple amethyst and yellow-orange citrine zones in a single crystal. Mined almost exclusively in Bolivia, its name blends "amethyst" and "citrine." This unique gem is also known as bolivianite and trystine in the gem trade.

Amethyst is the purple variety of quartz. Its name originates from the ancient Greek word "amethystos," meaning "not intoxicated," reflecting the belief it prevented drunkenness. A popular semiprecious gem, it is commonly found in geodes and used extensively in jewelry.

Alexandrite is a remarkable gemstone famed for its dramatic color change from green in daylight to red under incandescent light. This phenomenon is caused by chromium ions in its structure, which absorb specific yellow light, altering the perceived color based on the light source.

Agate is a common, banded variety of chalcedony, formed in volcanic rock nodules. While defined by its bands, some non-banded chalcedonies like moss agate share the name. A popular gem for millennia, it is often dyed to enhance its natural color for jewelry.