Minerals too small to see
Chalcedony is a generic term for compact, micro- or cryptocrystalline quartz, either translucent or mostly opaque. It is white when pure but much chalcedony contains trace elements of microscopic inclusions of other minerals, giving a wide range of colors.
Opal is an amorphous hardened hydrous silica gel that forms at low temperatures from silica-bearing circulating waters. Opal lacks a crystal structure and specific composition and is therefore not a mineral, but a mineraloid.
White Chalcedony - White, pure microcrystalline quartz
(Left) Cornwall, England & (right) Mexico City, Mexico
Size: (Left) 10 cm, (Right) 4cm
Agate - Translucent, multicolored chalcedony with concentric banding
Sao Paulo, Brazil & China
Size: Left :3.5 cm / Right: 8 cm
Onyx - Agate with black and white bands.
New Mexico, USA & Mexico City, Mexico
Size: Left: 2.5 cm / Middle:5 cm / Right: 1.5cm
Chrysoprase - Green variety of chalcedony colored by nickel oxide
Queensland, Australia
Size: 6 cm
Aventurine - Translucent chalcedony with small green fuchsite (mica) inclusions.
Bangkok, Thailand
Size: Rock : 12 cm / Gem: 9mm
Moss Agate - Contains green mineral inclusions and lacks concentric banding, giving it the appearance of moss.
Size: 20 cm
Jasper - Opaque, red to brown chalcedony
Cairo, Egypt & Ural, Russia
Size: Left: 2 cm / Right: 6 cm
Bloodstone - Green chalcedony with patches of red jasper resembling drops of blood.
India
Size: 6 cm
Opal & Opal Cabochon
Tectosilicates
SiO2
Queensland, Australia
Size: 7cm (Opal), 7mm (Opan cabochon)
Opal
Tectosilicates
SiO2
Queensland, Australia
Size: 10 cm
Opal
Tectosilicates
SiO2
Queensland, Australia
Size: 20 cm
Thundereggs
They are completely filled nodules of agate which form in silica-rich volcanic rocks, eg. rhyolites. As the molten volcanic lava cooled, steam and other gases trapped in the lava formed an expanding bubble. Later, silica-rich solutions may enter the cavity and fill it with banded agate or chalcedony.
Size: 20 cm