The grains that we use to play “milanesa” are born from the dismantling of rocks in a nearby mountain range. It is the same process that forms the sand in rivers, dunes, lakes and ponds – and that usually takes millions of years, from the erosion of a rock to the ride of the wind or the water from rivers to the beaches. The geographic origin of the sand can be in a mountain range a few meters or many kilometers from the beach. It’s the type of rock on that mountain that determines the type of sand you lie and roll on in the summer. “For example, that white and fine sand, common on the beaches of Brazil, is composed mainly of quartz, a mineral that comes from granite, one of the most abundant types of rock in the Serra do Mar, which borders the coast of the country”, says the geologist Paulo Gianinni, from USP.
What few people know is that, after appearing in the beach landscape for millions of years, the grains of sand also die. Everything happens right there on the beach: piled up by the enormous weight of the new layers of sand that continually reach the coast, the grain descends hundreds of meters deep and turns back into stone, forming the ocean floor.
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From stone to dust
Weathering of rocks is the first step in the formation of grains
1. The sand formation process begins with the action of wind, rain, roots and microorganisms on a stone, which geologists usually call “mother rock”. Over a period of millions of years, these agents sand down the stone, breaking it down into tiny particles.
2. These stone “remains” fall around the mother rock, mixing with the vegetation. The material that will compose the sand is already there, but until it changes its address, it is simply a type of soil
3. Sand formation proceeds with the transport of soil away from the parent rock. Under the action of wind, gravity and floodwaters, this mixture – now called sediment – flows down the mountain slope towards a river
4. By the action of the river water, the sediment is “sifted” between clay, sand and gravel. The clay is so light that it is suspended in water. The larger gravel is at the bottom and doesn’t even reach the beach. The sand, yes, has the ideal size to be carried by the current
5. Depending on the path and resistance of the mineral of origin, the grains may undergo a “ripening” and arrive smaller and more rounded on the beach. It is there that they will spend the next million years of their lives.
6. On the coast, the sand changes places because of the movement of the tides. And the sea and rivers also bring other ingredients to the mix, such as shells, seaweed and other animal remains that give the final sand formula.
from grain to grain
Rock origin determines sand color
BLACK SAND
GRAIN SIZE – 0.25 to 0.5 mm in diameter
MAIN COMPONENT – Mica
Angular grains (full of jagged, jagged bumps) like these are typical of dark sand beaches. In addition to blackening the sand, the mica signals that the place of origin of the sand is a mountain very close to the beach.
WHITE SAND
GRAIN SIZE – 1 to 2 mm in diameter
MAIN COMPONENT – Quartz
This is the type of sand present in a good part of the Brazilian coast. The fact that the grain is rounded and composed of quartz (a «by-product» of mica) shows that the rock that gave rise to the sand is relatively distant, as the grain has already suffered enough wear and tear.
MIXED SAND
GRAIN SIZE – 0.12 to 0.25 mm in diameter
MAIN COMPONENT – Silicon
The main mineral source of this sand is the irregular and whitish grains of silicon. But it also has a lot of coral fragments and red algae, which can give a stronger color to the mix.