Collect Rocks Day

What the day is

Collect Rocks Day is observed on September 16. It encourages people to start or add to a collection of rocks and minerals. The origin of the day is not documented, and it is a gentle, informal observance that suits children and adults.

Rock collecting needs no special equipment and no particular expertise. It can begin with a single interesting stone picked up on a walk, and the hobby grows from there.

Origin and background

Collectors choose rocks for all kinds of reasons: color, shape, texture, a sparkle, or the memory of where they found it. There is no right way to build a collection. Those who want to go further can learn to identify what they have, using a few simple tests.

The best known is the Mohs scale of hardness, devised by the German mineralogist Friedrich Mohs in 1812. It ranks minerals from one to ten by what can scratch what, from soft talc at one to diamond at ten. A fingernail scratches minerals up to about two and a half, a copper coin up to about three, and a steel knife blade up to about five and a half. Other quick tests include color, luster, and the streak a mineral leaves when rubbed on unglazed porcelain.

Rocks also have a cultural history. The fad of the Pet Rock in 1975, invented by the advertising man Gary Dahl, sold millions of ordinary stones in boxes with air holes and made him rich. A good rock, it seems, does not need to do anything.

Check the rules before you collect. Taking rocks is prohibited in national parks and many other protected areas, and on private land you need permission. Where it is allowed, take only a few, and leave the rest.

How to take part

• Pick up a few stones on your next walk, and wash and look at them closely at home.
• Label each one with where and when you found it, in an egg carton or a small box.
• Do a scratch test with a coin and a nail, and rank your rocks by hardness.
• Visit a rock and mineral show or a natural history museum.
• Trade a rock with a friend, which is how many a collection has grown.