Although cobalt blue spinels do owe their vivid color to traces of cobalt, it’s the color that makes them valuable, not the presence of that coloring agent. If your spinel has a rich saturated blue color, it is rare and valuable whether or not it contains traces of cobalt.
Sapphires treated by lattice diffusion generally cost less than sapphires that have been treated by heat without the addition of color-causing chemicals or sapphires that have not been treated.
Heating is an accepted treatment for sapphire. But for fine-quality sapphire, confirmation from an independent laboratory like NQTC that there is no evidence of heat adds to a sapphire’s rarity and value.
Look for eye-clean gems with lively, pleasing color and attractive cutting styles.
Jadeite is available in a wide range of colors. In rare cases some could be considered pink; however, this material is referred to in the trade as lavender. Rare examples of Guatemalan jadeite in a blue color do exist. Terms like pink jade, Mexican jade, Alaska jade, Transvaal jade or Japanese jade generally refer to other minerals, which may be green or other colors.
Although jewelers might expect amethyst from Siberia or Zambia to have better color than amethyst from Brazil, origin alone does not add value to amethyst. Value is based on quality, and color is the most important value factor regardless of country of origin.
In general, turquoise with a robin’s egg blue color is preferred. Unusual colors like yellow-green and pure green are in demand for use in inlay jewelry.
You should assume your ruby is heated. Rubies that have a report that confirms there is no evidence of heat from an independent laboratory like NQTC command a premium due to their rarity. Rubies that have been diffused or that are glass filled are worth less than heated rubies.
Not all Russian demantoids have these famous chrysotile inclusions. Horsetails are also seen in demantoids from Iran and Italy but not in those from Namibia or Madagascar.
Most biologists agree the Jurassic Park scenario isn’t possible, as any blood an insect was carrying would deteriorate rapidly and be contaminated with the insect’s DNA. However, scientists have extracted DNA from insects in 120-million-year-old amber.