Gemstones beginning with the letter "A"

Gemstone	Crystal System	Density	Hardness	Refractive index	Treatments
Alexandrite	orthorhombic	3.72	8.5	1.746-1.755	none
Agate	microcrystalline	2.66	6.5-7.0	1.544-1.553	dying
Amber	amorphous	1.08	2.0-2.5	1.54	heating, oiling, reconstitution
Amethyst	hexagonal	2.66	7	1.544-1.553	heating alters to citrine
Ametrine	hexagonal	2.66	7	1.544-1.553	none
Andalusite	orthorhombic	3.2	7.5	1.64 and 1.55	none
Aquamarine	hexagonal	2.72	7.5-8.0	1.577-1.583	heat
Azurite	monoclinic	3.7-3.8	3.5-4.0	1.730-1.838	none