MOLYBDENITE, M-450. Australia. 3/4 to 1-1/2 inch xls.
pure, no matrix or contaminate.  Average 6 to 12 grams per xl., sold
by weight or individual sample.   

MONTEBRASITE, M-455. South
Dakota. Nearly white cleavage masses. SL Check.

MONTICELLITE, M-460.  California.
Light olive green, compact, fine grained crystalline
masses. SL Check.

MONTMORILLONITE (BENTONITE), M-465
South Dakota. Gray clay masses - gravel size 
lumps. Because it decrepitates in the atmosphere, it is
packaged in individual plastic bags in sizes equivalent to
listed sizes. Check for availability.  (For other clay, see fire clay under sedimentary rocks.)

MUSCOVITE, M-470.South Dakota.
Silvery, vitreous mica cleavage books around 1" and
1/4 to 1/2 inch thick.  

NEPHELINE, NEPHELITE, M-480. 
Canada. Light gray. Greasy luster. 

OLIGOCLASE, M-485. Canada. White
cleavages of plagioclase that can show twinning striae. Check for availability.

OLIVINE, M-490 North Carolina, Light
to medium grass green or olive green, sugary crystalline
masses. 

OLIVINE, M-490A. Washington.
Granular to coarse crystalline, grayish green,
some interrupted cleavage faces. Near Forsterite
end of series. Check.

OLIVINE, Peridot.  Crystalline on basalt.  2" and larger only. AZ. 

OPAL, Opalite, M-495. 
California. Light gray, red, brown and
green, etc. Pearly to resinous common
opal. 

OPAL (DIATOMITE, DIATOMACEOUS
EARTH), M-500. California or Nevada. White
to light grayish, friable, earthy masses.  

ORPIMENT CRYSTALS, M- 505. Sold by weight. Nevada.
Pure yellow crystals with minor surface alteration. Xls sizes 2cm to almost 6cm.

ORPIMENT, M-505A.  Nevada.  Massive bright yellow with associated realgar.

ORTHOCLASE CRYSTALS, M-507.  Nevada & Colorado.  Excellent crystal samples

of this mineral.  Beige to pink to brown crystals averaging 1 inch in size.  Check. 

ORTHOCLASE - For other "Orthoclase" or Potassium feldspar, or K-Spar, see Microcline.

PHLOGOPITE MICA, M-510. 
Canada. Bronze to black cleavage book.  SL

PIRSSONITE, M-515. California. About
8 - 10 crystals about 1/4 inch (orthorhombic, translucent, gray)
 in a plastic envelope. Check

PLAGIOCLASE, see under ALBITE, ANDESINE,
ANORTHITE, LABRADORITE, OLIGOCLASE.

PLUMBOJAROSITE, M-520. Mexico.
Yellow-brown, earthy lumps and powder in
1 ounce bag. Check.

POTASH ALUM, M-525. Utah. Colorless
to buff groups of 2-30 mm octahedral
crystals. Around 3/4 inch to 1 inch pieces
available.  Check.  SL

PROBERTITE. M-530. California
Colorless, glassy, acicular crystalline
masses. Some with radial structure. SL