Warning: Amateur Geologist at Work

I got interested in geology from my hikes in the Grand Canyon and so I’ve been working to identify the rocky layers here in the Negev Desert. More specifically, I’ve focused on the geology of the Gan Hapsalim and Ein Avdat National Parks, which are just adjacent to our home in the Ben Gurion Midreshet. Unlike the Grand Canyon, most of the rock layers here are not so distinct. Many consist of varieties of limestone which I am unable to distinguish between. Anyway, here are the major formations I’ve been able to identify. More knowledgeable geologists than I are invited to submit comments and corrections below.

Sand

Covering most of the ground here is a layer of sand, which in some places forms into dunes, as pictured below. The dunes here aren’t soft like the ones in the Great Sand Dunes National Monument back in our home state of Colorado. Instead, they’ve been windblown and sun baked into a nearly rock hard consistency.

Composite Rocks

Just below the top layer of sand comes a layer of composite rock (pictured below). It largely consists of chunks of the layers below cemented together with what looks to me like either compacted sand, crumbled limestone, or a combination of the two. The stones within the composite, for the most part, seem to be similar in wear and size with the loose rubble in the dry river beds below.

Limestone
Limestone is typically deposited when an area is covered by a shallow sea. It largely consists of the shells of tiny ancient sea creatures that fall to the bottom when the creatures die. Limestone is amongst the softest sedimentary rocks and erodes into complex patterns. Most caves, for instance, are found in limestone formations. Here are a few examples of limestone formations in the Negev.

It’s common to find limestone formed into layers that separate and crumble in complex ways.

This ring pattern is widespread in the limestone in this area. I don’t know what forms it.

I frequently observe holes or pores in limestone that has been eroded by moving water.

Chalk

Chalk is a form of limestone that is deposited in relatively deep waters. It consists of microscopic plates shed by ancient microorganisms. Chalk is white and forms steep cliffs. It’s not clear to me yet where the other forms of local limestone end and the chalk begins. An excellent example of chalk can be found in the cliffs around Ein Avdat, a local spring that still features running water.

Here the chalk formation has been turned up on end so that the layers are eroding into spikes that resemble hair.

In this picture, running water from an ancient and long since dried up stream carved complicated patterns into the chalk.

Also, chalk is often eroded by water into smooth surfaces resembling soft serve ice cream.

Flint

The only rock I’ve found which provides relief to the unending vistas of limestone and chalk is flint. No surprise there, given that wherever you have limestone and chalk, you’re likely to also find flint. Because flint is composed of quartz, where the rocks are broken open, they appear glassy. Sometimes they are black and grey in color. They may also be quite colorful, containing reds, browns, whites, and greens as seen in the pictures below.

Because flint is so much harder than the surrounding limestone and chalk, it’s the only mineral around here that will take on a desert varnish (as seen in the pictures below). The varnish comes from minerals such as clay, iron oxide, and manganese oxides that accumulate on the surface of the rocks and then bake in the sun. The limestone and chalk are too soft to have a surface stable enough for varnish to form.

Flint typically forms in thin layers and nodules in limestone and chalk. Here’s an example of a stairstep formation caused by alternating layers of chalk and flint nodules (see picture below). Because the chalk is softer than the flint, the chalk layers erode out from underneath the flint layers. Eventually, the flint protrudes out enough that it breaks off, as shown in the close-up of the same formation below.