This piece of chalk comes in a small wooden box decorated with intricate ornaments. In the wooden box, besides the piece of chalk, there is also a small parchment with instructions on how to use the piece of chalk.
The owner can draw a circle with special ornaments on a flat surface and place an object in it which consumes a charge. Over the course of 10 minutes, the chalk particles on the surface are consumed and the person drawing the circle becomes aware of the magical properties of the object placed within it.
When found the Chalk has 1d6 + 2 charges.
Source: Homebrew (Magical Items)