How did the author of that hyperthetical book come by his assertions about the metaphysical properties of particular gemstones? Did he merely copy some of them from older, unverified sources?

There are are 3 main attitudes towards the assertions regarding particular gemstone metaphysical properties. Some, perhaps over influenced by the materialist viewpoint, blindly reject any idea that suggests gemstones might have any metaphysical properties. Others blindly believe any fantastic tale that they are told about the properties of gemstones. A third group of people neither blindly reject nor accept the assertions. They attempt to investigate the subject via scientific And metascientific techniques as deeply as possible. That is the approach of VirtueScience. Let us then list the basic methods of investigation:

Channeled Sources

Intuition

Symbolic Physical Properties

Ancient Wisdom

Extraterestrial Wisdom

Prayer and Meditation

Dreams and Dream Work

Worked out from Known Properties of it's Chemical Elements

From the Words of a Trusted Adept

Via Experimentation

Correlating Transcultural Themes

Books about Gemstones