Packing the sample

Original non-fiction-style practice text.

At the end of our survey, a visitor brought a piece of dark stone to the field tent. It contained a bright stripe like the mineral we had spent a week looking for. He said he had found it near the eastern ridge, but he had walked several paths that afternoon and could not identify the spot. The stone had travelled loose in his bag beside specimens bought from a roadside stall.

Our team leader, Arun, thanked him and put it in a separate tray. He did not add it to the numbered bags from our own survey. Each of those bags recorded a precise location, the time of collection and the name of the collector. We also photographed the rock before removing it. The attractive visitor's sample had none of this supporting information.

One assistant objected that it might still be the most interesting discovery of the trip. Arun agreed. He was willing to examine it, but unwilling to claim it proved that the mineral occurred on the eastern ridge. Instead, he marked the suggested area on the following day's search plan. The object could give us a useful lead without providing a dependable conclusion. If we found a matching specimen in place, its unremarkable numbered bag would matter more than the sparkle that had first caught our attention.

Explain, using your own words, why Arun would not use the visitor’s stone as proof that the mineral occurred on the eastern ridge. Give three reasons.