Lammas is one of the Wiccan Sabbats, and is a cross-quarter day between summer and autumn, a time when the first fruits of the planting season can be harvested. It is all about harvesting, abundance, being grateful for the Sun, and honoring the god Lugh.
These crystals and gems have many properties. The one quality that they all have in common is that they attract money and/or prosperity. Choose the ones that speak to you. Place them on the altar or wear them during your ritual. If you have enough, use them to create your magickal circle.