Hi,
As a non-gemologist, I found this Online Handbook called "Handbook for the Gem Buyer - Preface and Table of Content
by Sondra Francis, G.G. - © Gem Dealers' Secrets - Handbook for the Gem Buyer" to be quite fascinating.

This is the Table of Contents [below].
Each 'subject label' is 'clickable' [at the Ganoksin Website -
http://www.ganoksin.com/borisat/nenam/contents.htm and takes you to excellent info for someone who wants to know 'more', but doesn't want to get bogged down in too much heavy info.
Table of ContentPart I - The Make-Up of a GemstoneThe Joy of Gems
The Formation of Gem Materials
Optical and Physical Properties of Gemstones
The Four C's Plus One
The Treatment of Gemstones
Part II - The Personality of GemstonesGemstone Name Reference List
When You are Ready to Buy
Andalusite
Beryls: Aquamarine, Emerald, Morganite
Chrysoberyl: Alexandrite and Catseye
Cordierite: Iolite
Corundum: Rubies and Sapphires
Diamonds
Feldspars: Moonstones, Labradorite
Garnets: Almandine, Pyrope, Spessartine, Rhodolite, Grossular, Andradite
Jades: Jadeite and Nephrite
Lapis Lazuli
Olivine: Peridot
Opals
Pearls, Cultured Pearls
Quartz: Amethyst, Citrine, Chalcedonies, Agates, Chrysoprase, Bloodstones
Spinel
Spodumene: Kunzite and Hiddenite
Topaz
Tourmaline: Rubellite and Indicolite
Turquoise
Zircon
Zoisite: Tanzanite
Other Gemstones of Interest
Man-Made Gem Materials
Part III - Helpful Information
Birthstones and Anniversary Stones
Glossary