option: (config?)

• discard stone materials / do not add to data set
• accept stone layers as things to map
• re-enable deletion of entries

It only happens to rock samples, which are being aggregated per-chunk as it stands.
=> small memory/file size footprint.

As part of the server-side nature of all rock samples, discarding the default rocks (which should be the only basic stones) is easy and appropriate.

The stone layer rocks are not default rocks.
Different filtering will be required.