yellow diamond
It is called the Chintamani Stone.
Amethyst.
An inferior gem-stone diamond is still called a diamond, and based on its cut, colour, carat weight and clarity, may not be of the highest quality. Non gem-stone diamonds are called industrial diamonds.
Maryland has an Official Gem which is an agate called the Patixent River Stone but it has no Official Stone, Rock or Mineral.
The flat face of a gem is called a table. It is the largest flat facet on the top of the gemstone, usually found in the center of the stone.
I would say Citrine, a nice yellow semiprecious gem. You might prefer Quartz, or even Feldspar for something different.
Blazing Shard, Blazing Stone, Blazing Gem, Blazing Crystal. Frost Shard, Frost Stone, Frost Gem, Frost Crystal. Lightning Shard, Lightning Stone, Lightning Gem, Lightning Crystal. Lucid Shard, Lucid Stone, Lucid Gem, Lucid Crystal. Power Shard, Power Stone, Power Gem, Power Crystal. Dark Shard, Dark Stone, Dark Gem, Dark Crystal. Dense Shard, Dense Stone, Dense Gem, Dense Crystal. Twilight Shard, Twilight Stone, Twilight Gem, Twilight Crystal. Mythril Shard, Mythril Stone, Mythril Gem, Mythril Crystal. Bright Shard, Bright Stone, Bright Gem, Bright Crystal. Energy Shard, Enerfy Stone, Energy Gem, Energy Crystal. Serenity Shard, Serenity Stone, Serenity Gem, Serenity Crystal. Orichalcum, Orichalcum+
gem stone
You may be thinking about wulfenite. The mineral was named after Franz Xavier von Wulfen, an Austrian mineralogist who lived between 1728 and 1805. The color of the mineral ranges from yellow and yellow-gray to orange-red.1
It is a semi-preaous gem stone
a gem, a gem stone and a sparkly rock. (?)