Case File: Rock n' Research


To identify what type of rock I had and where it came from - M & R Bates , Piedmont, NJ


My father was a collector of strange objects—and the deck he built outside the family house was made up of "found" rocks he brought from various places.

I've always been fascinated by three of them which he said he brought from a trip he took out West.

These rocks are dark grey in color, one of which has some round dark greenish lumps running through it.

Your show piqued my interest in rock and mineral identification and so I thought I'd try my skills out.

The Web sure made research a lot easier. Question and Answer flow charts helped me identify my rock, but it required the observation skills a good rockhound needs.

The questions were basic, beginning with "is the rock made of crystal grains?" As it didn't have any shiny faces or flat areas, I knew I could rule that out.

I kept running out to the rock to answer my questions: no, it didn't have bubbles in it; it didn't look like black glass; and a nail I used to scratch a discrete area of it with didn't produce any sand.

The next question required me to chisel a small piece of the rock off to see if it scratched glass. Laying a piece of glass on a flat surface I attempted to scratch the glass with my rock chip. No luck, the rock wasn't able to.

Finally I was asked what color the rock was and I clicked black and grey. And, I discovered my rock was one of the basics: basalt, an igneous rock.

I decided to try and find out where my rock came from, so I went to the local library and researched online which led me to believe they were from right here in New Jersey, crossroads of the Ice Age.

I had no idea how geologically diverse my state was. My region, the Piedmont area of northwestern New Jersey rests on rock created in the Late Triassic and Early Jurassic periods, some 230 to 190 billion years ago.

Basalt is formed in areas where tectonic plates move-which is just what happened here when the Atlantic Ocean was formed.

As the earth's crust got stretched in these areas, fault lines formed along with rift valleys.

Pressure built up under the surface, and the pressure caused the earth's mantle to melt and rise to the surface where it slowly cooled, forming the rocks I found in my backyard.

Perhaps it isn't the most interesting rock to look at—I certainly love imagining what the area that is now my backyard must have looked like billions of years ago when volcanoes were bubbling away.

Related Content