Mineral Of The Day

Mineral Of The Day #155: Rutile

Mohs Hardness Scale: 6-6.5
Category: Oxide mineral
Formula: TiO₂

Fun Facts:

• Named for the Latin rutilus, red, in reference to the deep red color of some specimens when viewed by transmitted light.
• Rutile is used in the manufacture of refractory ceramics and for the production of titanium metal.
• Finely powdered rutile is used a brilliant white pigment!
• Rutile is used in sunscreen to protect against UV induced skin damage.
• Small rutile needles present in gems create an optical phenomenon known as asterism. Asterated gems are known as “star” gems (star sapphires, star rubies, etc.).

Mineral Of The Day #147: Carnelian

Mohs Hardness Scale: 6-7
Category: silicate mineral, chalcedony variety
Formula: SiO₂

Fun Facts:

• Carnelian is a brownish-red mineral commonly used as a semi-precious gemstone.
• Its color varies greatly from pale-orange to an intense almost-black coloration.
• It was used in decorative arts in 1800 B.C. by the Minoan civilization.
• Carnelian was used during Roman times to make signet rings imprinting a seal with wax on correspondence or other important documents. Hot wax does not stick to carnelian.
• It gets its name from the Persian word sered, meaning yellowish-red.

Happy Gemstone Thursday! Happy birthday wishes go out to MOTD Team Member, Sandra and DOTD (Dad Of The Day), Steve!

Mineral Of The Day #126: Realgar

Mohs Hardness Scale: 1.5-2
Category: sulfide mineral
Formula: As₄S₄ or AsS

Fun Facts:

• Realgar gets its name from the Arabic rahj al gar, which means “powder of the mine.”
• It is also known as “ruby sulfur” or “ruby of arsenic.”
• Realgar, along with orpiment and arsenopyrite, provide nearly all of the world’s supply of arsenic.
• It was used by firework manufacturers to create the color white in fireworks!
• Historically, realgar was used as a pigment and a medicine in the Roman Empire.
• Realgar is one of the few sulfides that is not metallic, opaque, or blandly-colored!
• Realgar specimens should be stored in dark, enclosed containers and only exposed to light for brief encounters because they will break down and eventually become a powder over time.

Mineral Of The Day #97: Oligoclase

Mohs Hardness Scale: 6-6.5
Category: tectosilicate mineral, feldspar group
Formula: (Ca,Na)(Al,Si)₄O₈, where Ca/(Ca + Na) (% Anorthite) is between 10%-30%

Fun Facts:

• Oligoclase is a rock-forming mineral that is usually white with shades of red, grey, or green.
• It is named for the Greek oligos (little) and kasein (to break).
• Perfectly colorless and transparent oligoclase has been occasionally faceted as a gemstone. A red gemstone called sunstone is oligoclase with flashes of reddish color caused by inclusions of hematite.

An old (albeit enthusiastic!) note was found with the first specimen pictured above. It reads:

Sunstone deep pink

If you can get the right light on this, it is superlatively gorgeous. You seem to see miles down into it in a blaze of fire.

Black = magnetite

Mineral Of The Day #87: Crocoite

Mohs Hardness Scale: 2.5-3
Category: chromate mineral
Formula: PbCrO₄

Fun Facts:

• Crocoite was discovered in 1766. It was originally named “crocoise” from the Greek crocon (meaning “saffron”), an allusion to its color.
• Crocoite is the official Tasmanian mineral emblem.
• It is known for its distinctive orange-red color.
• It was once a main ore of chromium, but it is now too rare to be used. It is sought after by mineral collectors due to its attractive color.

Mineral Of The Day #86: Chalcotrichite

Mohs Hardness Scale: 3.5-4
Category: oxide mineral
Formula: Cu₂O

Fun Facts:

• Chalcotrichite is a variety of cuprite consisting of thin fibrous sprays or mats of hair-like crystals.
• Its name comes from the Greek meaning “hairy copper.”
• It is popular as a mineral specimen.