i believe that quartz is silica !!!!
Quartz
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For other uses, see
Quartz (disambiguation).
Quartz 
General Category Mineral
Chemical formula Silica (silicon dioxide, SiO2) Identification Color Clear (if no impurities); also see Varieties
Crystal habit 6-sided prism ending in 6-sided pyramid (typical)
Crystal system rhombohedral class 32
Twinning Dauphine law, Brazil law and Japan law
Cleavage None
Fracture Conchoidal
Mohs Scale hardness 7 - lower in impure varieties
Luster Vitreous/glossy
Refractive index nω = 1.543 - 1.545 nε = 1.552 - 1.554 Optical Properties Uniaxial (+)
Birefringence +0.009 (B-G interval)
Pleochroism None
Streak White
Specific gravity 2.65 constant; variable in impure varieties
Melting point 1650 (±75) °C
Solubility H2O insoluble Diaphaneity Transparent to translucent Other Characteristics Piezoelectric
Quartz (from
German Quarz (
help·
info)
[1]) is the second most common
mineral in the
Earth's
continental crust,
feldspar being the first. It is made up of a
lattice of
silica (
SiO2)
tetrahedra. Quartz has a hardness of 7 on the
Mohs scale and a
density of 2.65 g/cm³.
sand
The most common constituent of sand, in inland continental settings and non-
tropical coastal settings, is
silica (silicon dioxide, or SiO2), usually in the form of
quartz, which, because of its chemical inertness and considerable hardness, is resistant to
weathering.
The composition of sand is highly variable, depending on the local rock sources and conditions. The bright
white sands found in tropical and subtropical coastal settings are eroded
limestone and may contain coral and shell fragments in addition to other organic or organically derived fragmental material.
[1] The
gypsum sand dunes of the
White Sands National Monument in
New Mexico are famous for their bright, white color.
Arkose is a sand or
sandstone with considerable
feldspar content, derived from the
weathering and
erosion of a (usually nearby)
granite. Some sands contain
magnetite,
chlorite,
glauconite or
gypsum. Sands rich in magnetite are dark to black in color, as are sands derived from volcanic basalts and
obsidian. Chlorite-glauconite bearing sands are typically green in color, as are sands derived from basalt (
lava) with a high
olivine content. Many sands, especially those found extensively in
Southern Europe, have
iron impurities within the quartz
crystals of the sand, giving a deep yellow colour. Sand deposits in some areas contain
garnets and other resistant minerals, including some small
gemstones.
Sand is transported by wind and water and deposited in the form of
beaches,
dunes,
sand spits,
sand bars and related features.
.
