I second all of these suggestions above but I'd like to add one: Sapphire. It's never mentioned here because it can be pricey. But there are small and cheap ones, too. You don't need to get a huge flawless jewel to enjoy the properties of it.
I have a small cheap one set in Silver. I think mine was from Etsy. Sapphire comes in many shades of blue (and yellow). Some are really pretty watery blue.
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from Crystalvaults web page: Stone of Wisdom, a royal stone of learning, mental acuity and psychic activation, a seeker after spiritual truth. Its pure Blue Ray brings order and healing to the mind, lending strength and focus, and an ability to see beneath surface appearances to underlying truths and to utilize that knowledge. It stimulates the Throat and Third Eye Chakras, allowing one to access deeper levels of consciousness in order to gain a fuller understanding of self. Associated with the planet Saturn, Blue Sapphire embraces order, structure, and self-discipline, and is ideal for accomplishing goals and manifesting ideas into form. Sapphire’s power to transmute negative thoughts and energy also makes it highly effective for earth and chakra healing.