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It's just another way of saying "be useful". When you are in the woods a map and compass would be of use. They would be useful.
Someone that is looking to purchase quartz worktops can purchase them at local stores such as Canadian Tire or Home Depot. For someone that would prefer to shop online, the can do so at the website eBay.
This would be quartz.
Why would you want to know I hope your not planning to poison someone
Quartz is a mineral not a rock. Fossils can be found associated with quartz in sedimentary rock not inside the quartz.
Olivine would weather faster than quartz
Quartz
If someone wishes to persue a career in US politics it would be useful if they undertook a degree in American Studies as it provides them with useful information about American studies.
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A magnetic sweeper would be useful in a situation when someone needs to pick up and find metal items, such as iron. This may be useful in steel work companies.
Quartz because its harder than calcite and the quartz in thicker.
Perhaps common salt, for it is readily available and easily observed. Otherwise, a quartz crystal would also be common and attractive, and a useful size.