Rehoboth Beach EarthCache

1a: Take a small sample of sand in your hand and look at it under your magnifying glass. What colors do you see?

1b: Estimate the percentage of quartz and feldspar present.

2a: Pour some vinegar on the sand. Does it react?

2b: What does this say about the presence of Calcium Carbonate?

3a: Rub your magnet against a new sample of sand. Does anything attract?

3b: What does this say about the presence of Iron or the origin of the sand?

4: Post a pic of you or a signature item with the historical marker, gazebo, fountain or anything that says Rehoboth Beach in the background. You don't need to include your face in the pic if you don't want to. You can also send me the pic through messenger if you don't want to post it with your log.

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LOCAL GEOLOGY

Rehoboth Beach's geology consists of unconsolidated sediments, specifically sands and gravels, characteristic of the Atlantic Coastal Plain and its Delaware Bay Group deposits, which formed from material eroded from the Appalachian Mountains over the past 120 million years.

Atlantic Coastal Plain

The Atlantic Coastal Plain is a broad, low-lying, and mostly flat region of the eastern United States, extending from Massachusetts to Florida, formed by sediments deposited by rivers from the Appalachian Mountains and the rising and falling sea levels of the Atlantic Ocean. This region is characterized by rivers, marshes, and swamps, with the terrain sloping gently toward the ocean

Delaware Bay Group

The Delaware Bay Group is a stratigraphic unit in southern Delaware comprising Middle to Late Pleistocene interglacial deposits, specifically the Lynch Heights and Scotts Corners formations. These formations represent swamp to nearshore sediments deposited as sea levels rose and fell along the margins of an ancient Delaware Bay, influenced by regional crustal subsidence and changes in global sea level. The Delaware Bay Group is one of three groups of interglacial deposits, alongside the Assawoman Bay and Nanticoke River Groups, all recognized by the Delaware Geological Survey.

HOW SAND FORMS

Over vast periods, rocks, in this case from the Appalachian Mountains, break down due to natural forces like wind and water. Rivers and streams carry these broken-down rock particles downstream toward the ocean. As the sediment travels, it gets further ground down and sorted by the force of the water, eventually forming sand. The ocean then deposits these tiny rock and shell fragments onto the shore, creating the beaches we see today.

BEACH SAND

Beach sand is a granular material primarily composed of durable minerals like quartz (silicon dioxide) and feldspar from eroded land rocks, though its specific composition varies by location. Depending on the local geology and ocean conditions, beach sands can also include volcanic material, like obsidian and basalt in volcanic areas, or be rich in calcium carbonate from the shells and skeletons of marine organisms in tropical regions.

SAND COMPONENTS

Quartz: The most common mineral in sand, it is a very hard and resistant form of silica (silicon and oxygen) that forms from the weathering and erosion of inland rocks. Under a magnifying glass, quartz appears transparent, glassy or clear

Feldspar: Another common mineral found in eroded inland rocks, feldspar is a tan-colored mineral that is harder than most other minerals and resists weathering, contributing to the typical color of sandy beaches.

Calcium Carbonate: Beaches are often formed from calcium carbonate, which comes from the broken-down shells and skeletons of marine organisms. Vinegar reacts with the calcium carbonate present in shells and other biological components of beach sand, producing visible carbon dioxide bubbles. This fizzing indicates the presence of biogenic sand, whereas sand composed of abiogenic minerals like quartz will show little to no reaction with the weak acid in vinegar.

Volcanic or Basaltic Sand: Derived from basaltic volcanic rock, which is rich in iron, giving the sand a dark or even black color. The presence of iron can easily be detected with a magnet.

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