Compacted Spherules at "Kirkwood" - Sol 3046 (Absolute Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga/Lunar Explorer Italia/Italian Planetary Foundation)

Caption NASA:"Small Spherical Objects fill the field in this mosaic combining 4 (four) images from the Microscopic Imager onboard the NASA - Mars Exploration Rover (MER) Opportunity. The view covers an area about 2,4" (inches, such as about 6 centimeters) across, at a Rocky Outcrop known as "Kirkwood" and located in the Cape York Segment of the Western Rim of Endeavour Crater. The individual Spherules are up to about one-eighth of one inch (such as approx. 3 millimeters) in diameter. The Microscopic Imager took the component images during the 3064th Martian Day, or Sol, of Opportunity's work on Mars (such as September 6, 2012).
It has to be remembered that the MER Opportunity already discovered Martian Spherules at its Landing Site, more than eight-and-a-half years ago and those Spherules were nicknamed "Blueberries". They provided important evidence about long gone "Wet Environmental Conditions" on Mars because researchers using Opportunity's science instruments identified them as "Rocky Concretions" rich in the Mineral Hematite deposited by Water saturating the Bedrock.
However, the Spherules at Kirkwood do not have the Iron-rich composition of the Blueberries and they also differ in concentration, distribution and structure. Some of the Spherules in this image have been partially eroded away, revealing a "Concentric Internal Structure". Opportunity's Science Team plans to use Opportunity for further investigation of these Spherules in order to determine what evidence they can provide about the (VERY) ancient Martian Environmental Conditions.