Determining if sand is silica based?

[EyesClosed]

Does anyone know of how to determine if sand is silica or calcium carbonate?

There's a beach near me that apparently has one of the finest sands in the world, and there is a cool water reef nearby. I want to make 100% that the sand from there is not silica, anyone know how to determine?

 

[MattM]

A few drops of hydrochloric acid.

Fizz = carbonates. No fizz = silicates.

 

[jandree22]

A few drops of hydrochloric acid.

8O :lol:

Vinegar works too :wink:

 

[EyesClosed]

ok, so put a few drops of vinegar, and if theres a fizz, then thats calcium carb. Fizz, as in audiably, or bubbles?

 

[Juck]

Silica sand is mostly crystalline,,, aragonite sand is opaque white.

 

[jandree22]

it's audible if you get your ear RIGHT next to it. You'll be able to see really really tiny bubbles form.

 

[kim]

Vinegar, acetic acid, lemon juice......if it contains carbonate it will look like a seltzer (I think you have them....for upset tummies ?). You will be able to see if some, most or all of the grains are fizzing.

I've used this in the past....once you see it it is very clear.

If you find that the sand is NOT carbonate based, put some in RO water for a few days and test for silicates. Silica sand (quartz) will not dissolve, but if there are extensive impurities (eg silicate-based clays) you might see some positive results and need to consider those. Do they wash out after a while, or are there enough to keep coming at you...? If this is beach sand, I would expect that soluble stuff has already been dissolved but I don't know your geology. Play safe !

As an example, Natures Ocean Fine Marine White (a commercial silica sand) gave me a reading of 2 ppm after soaking about 50 g in 250 g of RO, but after a few flushes the impurities had gone.

kim

ps make sure the water you use is silicate free to start with....I boo boo'd on that first time around..

 

[AnotherGoldenTeapot]

Worried about diatoms?

FWIW I have about 2 inches of very fine silica sand at the bottom of one of my tanks, this in turn is covered with about one inch of shells.

I have no diatoms - or at least, no visible evidence of any.

In USD for a 6' x 2' tank I spent under $10 on this media for the bottom. It looks great (especially the shells once they grew some coraline).

The shells (off topic I know) are great - basically creates a refugium in the main tank.