Possible Clues:

• July birthstone
• Hoax involving Russia's foremost essayist's a gem
• Dull red stone; lone cairn (anagram)
• Sentimental stuff by Lamb that could be seen as a gem?
• Banal piece by essayist? It's a gem
• Something trite at start of Alien, otherwise a gem
• Gemstone Scotsman found by dog-wood
• Fasten back after breaking off end of corner stone
• Gemstone Scotsman found under dogwood tree