The Fresnel Lens is a custom item that will turn Granite or Polished Granite into Obsidian or Lava, and Cobblestone or Stone into Lava.

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To use the Fresnel Lens:

1. Make sure it's daytime (it needs sunlight to work)
2. Right-click in front of the Fresnel Lens with a Granite, Polished Granite, Cobblestone, or Stone block
3. After about 20 seconds, the block will melt into "Lava"
4. You can collect the lava at this point by right-clicking it with an empty bucket or Clay Bucket.
5. If you placed Granite or Polished Granite, after about 5 more seconds, the lava will cool into Obsidian.
6. Right-click the Obsidian to collect it.

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What is a Fresnel Lens and what does it have to do with Obsidian?

A Fresnel Lens is a special lens that can either capture a large area of light and focus it into a single point, or take a small area of light and disperse it over a larger area. When focusing a large area of sunlight into a point, it can generate temperatures hot enough to melt some rocks (upwards of 2,300°f). This can be used, in real life, to melt Granite. Granite is a felsic igneous rock; felsic meaning it contains quartz and feldspar, igneous meaning it was formed by the solidification of magma or lava. Obsidian is formed when felsic lava cools rapidly with very little crystal formation. In other words, you can use a Fresnel Lens in real life to melt Granite, then rapidly cool it to form Obsidian. SCIENCE!