The Continent of Africa has a great variety of corundum localities; and some of the least known produce some of the finest specimens.   Many seem to contain no gems; but produce large, euhedral crystals or clusters, attractive in any display.  As you look at a few of our favorite African specimens, see if you do not agree.
Sierra Leone, Guinea:  The Mano River flows into the Atlantic Ocean, forming part of the border between Sierra Leone and Guinea along the way.  Local miners dig into the riparian gravel bars for diamonds, and recently started to recover corundum crystals from the overlying strata.  Regional geology and water wear indicate that lode sources may be as far away as Liberia.
These crystals can be a fine, highly translucent purplish lilac; making them ideal for carvings and cabochons.  Though some appear asterated, I have not seen any produce good stars.  Here are four specimens from the collection.  These came from Guinea.
On the left is a strange "black ruby" corundum river cobble found near Kono (Sedafu), Sierra Leone.   Blue and white corundums, some weighing several pounds, as well as particolored ones, are occasionally found  in the same general area (right).   
Kenya and Uganda:
The 1,105 carat cluster ("The Ugandan Road Kill Pigeon") and cluster on the left came from the "Pokot" Region, along the Kenya/Uganda border.  The specimen on the right, from Kwale, has two interpenetrant twins (two views shown).  All three crystals are doubly terminated.  
Longido is the name given to the region producing the classic red and green "ruby in zoisite".  Artisans can use the interplay to produce attractive carvings; but to this collector, the "hex outline" is a favorite (far left below).
  Large gemmy crystals (near left) are rare.  The specimen on the right is allegedly one of the original pieces found during the World War I battle that opened up the ground and led to the discovery, and is ex coll. John Saul.  [Researching the truth of such romantic stories is what makes this project so interesting.]  
The facetable ruby on the far left is from the Mayote Mine, Mahenge.  Next to it is a ruby cluster from Morogoro.  On the right are (L to R) sapphires from Songea, Tunduru, and the Umba Valley.
"Z" Localities:  Large semitranslucent crystals of medium blue corundum, are often of "textbook" hexagonal prismatic form, exhibiting superb vicinal forms on the basal pinacoid (neat raised triangles on both ends).  Older specimens were commonly alleged to be from Mozambique or Zambia; but recently the identically appearing material is coming reportedly from the vicinity of Breitbridge, Zimbabwe. On the left are two oldies (Zambia or Mozambique). The flat surface on the second appears to be a natural termination. On the right
 are  a fine regular hexagonal prism and a unique offset one (both nicely terminated; the latter a gift of Cathy Parisi), recently mined (Zimbabwe).  At the far right is a rare Zimbabwe bitapered ruby crystal.
South Africa  
  The Zoutspansburg Hills produced the two elongated prisms to the left.  The smaller one is doubly terminated.  The record for a sapphire crystal (355 pounds) is apparently held by one from here; but I understand you have to go to Johannesburg to see it.  Two other Transvaal specimens appear on the right. ( Near right ex coll. Louis Zara.)  
Storage bin:
First Row:  (1) Sierra Leone, (2) Tanzania (ruby and diopside), (3) Transvaal (ruby in sillimanite), (4) and (5) South Africa (different specimens),
Second Row:  (6) Suite of specimens from Somalia (top left ex coll. John Saul, others are gift of James Butterbrodt), (7) and (8) Huge sapphire boulder from Africa which may be coming to America - note interesting polygonal blue/white color zoning.



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