The Beach Sand of the Gulf of Mexico

The beaches on the Gulf of Mexico are famous for their crystal clean water and sugar white sand.  Siesta key beach received numerous awards for its soft, clean, pure-white sand.  The Siesta beach ranks the number one beach in Dr. Beach's top 10 beach list again this year.  Unlike most beaches that are composed of crushed shells, rocks or lava, the powdery sand found on the Siesta Beach is pure white and finer in texture than most refined sugar. Harvard University's geology department found the sand of Siesta Beach was 99% pure quartz.
During the spring break, we had a chance to visit several beaches on the Gulf of Mexico on a camping trip.  We collected some beach sand from each park on the trip (Figure 1): The Gulf State Park, Alabama, Henderson State Park, Florida and Siesta Key, Florida (We visit all three beaches on the key: Siesta, Crescent and Turtle beach).  I check them out on my microscope.  Are they as good as claimed?

Figure 1. Beach sand collection sites on our camping trip

Figure 2. Sand collected from Siesta Beach, FL

Of all beaches on our camping trip, the sand on the Siesta beach appears to be the whitest.  The sand is also very soft to touch.   It has powdery feel when I rub them between my figures.  The images under the microscope explain the the color and soft touch.  The sand crystals are almost all quartz and completely transparent with very few impurities.  The small and uniform in size also explains the powdery and soft touch.  (Note: The images under the microscope are sparkling. It looks much better than the pictures show - To be fairly compared with other sand specimens, I fixed the ISO and exposure time while taking the picture.  The whiteness of the sand caused the picture to be over-exposed.)

Figure 3. Sand collected from Crescent Beach, FL

On the same key as the Siesta beach, the Crescent beach is slightly to the south of Siesta beach.  The color of the beach sand is almost as white as the sand on Siesta beach and have the same soft, powdery feel.  Under the microscope, they appears almost the same as the sands from Siesta beach.  The slightly more yellowish color is barely noticeable unless I put the picture side by side.

Figure 4. Sand collected from turtle beach, FL

The turtle beach is located on the south end of the Siesta key.  The sand is very dark and  coarse.  There are plenty of sea shells on the beach.  There is no surprise to see that there are plenty of sand made of sea shells.   There are very few quartz crystal found in the sand collected from Turtle beach.

Figure 5 Sand collected from Henderson State Park, FL

Henderson State Park beach is located between Pensacola and Panama city.  The area is famous for its Emerald green ocean.  The sand is sugar white but the sand crystal is more granular than the sand collected from Siesta or Crescent beach.  Like the Siesta or Crescent beach, the sand is almost completely consist of transparent quartz.  The quartz crystal is also larger.

Figure 6. Sand collected from Gulf State Park, AL

The color of the beach on Gulf State Park, AL appears to be more yellowish.  The sand is still be but not as powdery as the sand found on Siesta or Crescent beach.  The sand crystals appear to have more impurities and less transparent. 

Figure 7. Sand collected from Gulf State Park playground

Interesting sand we found in the playground of the Gulf State Park.  There are purple, green and blue particles in the sand.  Out of curiosity, we collected some sand from the play ground and looked at them under a stereo microscope.  They appears to be quartz but stained with different.  The sands seem to have more round edges caused by the weathering.  They appears to be different from the sand collected on the beach.

That's just about my general impression about the same.  Can the number tell me the same story?

The whitenss appears to be consistant with the purity of the quartz crystal found in the beach sand. I took three pictures for each collection by randomly selecting three different areas of the sand specimen.  The number of quartz crystals that are completely transparent, semi-transparent (milk white or yellowish) or none-quartz particles - nice summer project for my kids.  Megan helped out a lot for counting the crystals.

Figure 8. Counting the number of completely particles in the same specimen.  The picture shows the sand specimen collected from Gulf State Park, AL.  The completely clear quartz crystals are striked with green lines while the impurities are circled.

The beach sand collected from Siesta (1142/1149; quartz particles/all particles), Crescent (1144/1152), Henderson State Park (268/270) and Gulf State Park (446/449) beach all have over 99% of quartz.  The percentage goes down to 93% (419 / 449) for Gulf State Park if I only included completely transparent quartz crystals.  The sand from Turtle beach is completely opposite of others.  It contains only 2.5% of quartz (3/114).

Figure 9 Measure the size of particle with TSView image microscope

image acquisition and measuring software

The granunality of the sand can be measured by the size of the sand particle.  Using microscope calibration slide to obtain the conversion factor between pixels and micrometer, I can convert the size of the sand particles in the digital image from pixel to micrometer.  I sampled the particles by drawing a line diagnally and measure the length of any particles across the line.  The average size of the sands from Siesta and Crescent beach (197 and 194 um, respectively) are the smallest among all specimens.  Followed by Gulf State Park and Henderson State Park (386 and 509 um).  The tutle beach sand has the largest average crystal size among all parks (900 um).