Report: Sagenites in “The Carver” Texas Agate Field

I am finding lots of sagenitic agates and sagenitic material in the nodules, geodes, and vein agates from ‘The Carver’ agate field.  When cut, the sagenitic material appears as radiating needle-like inclusions often resembling a star burst or sun flower.

So what is sagenite?  Technically, it is not a type of rock but an inclusion appearing in a rock specimen.  Sagenitic agate is a radiating needle-like structure encased in a quartz or chalcedony nodule, geode, or vein agate.  The radiating needles are often iron mineralization appearing as a black or dark brown color, however, yellow and other colors are often observed.  These other colors are the result of mineralization other than iron.  Sagenitic agate, like many other types of agate, does not technically meet the agate definition which requires among other things, banding.  Accordingly, sagenitic agate, like moss agate and dendritic agate, lacks banding and is definitionally not a true agate.

The sagenitic radiating needles most commonly form near the outer rind or surface of the nodule, geode, or vein agate.  It appears that they have  a propensity to be formed near the contact zone between the nodule and the lava in which the nodule formed.  Having said this, however, radiating sagenitic needles also appear deep within the silica of nodules away from the rind.   While silica/quartz/chalcedony usually make up the majority of the volume of a nodule or geode, there are instances where the sagenitic needles make up most of the nodule or geode.  Some nodules/geodes are literally filled with dozens of small radiating sagenitic needle-like structures, while others have a single large one.

More photographs of sagenitic agates and structures can be seen in the galleries here at the website.

John Carver

PHOTOS and SPECIMENS (all by John Carver and from ‘The Carver’)

Rock #749
#749 – Multicolored sagenites, probably not iron mineralization
Rock #789
#789 – Sagenites clustered together resembling sunflowers
Rock #790
#790 – Radiating needles probably due to iron mineralization responsible for dark colorization
Rock #1051
#1051 – Radiating needles around the entire rind of the nodule encompassing most of the nodule’s volume
Rock #1293
#1293 – Multicolored fanlike sagenites resembling fireworks starburst
#2486 – Multiple sagenitic growths
#2854 – Two yellow sagenitic growths encompassing most of the nodule
#2954 – Multiple sagenitic growths randomly spaced within chalcedony nodule