130 THE ROMAN COMAGMATIC REGION. 
Apatite. Groundmass: about i per cent or less, 0.02 to 0.05 mm., subhedral, prismatic, 
difficult to detect. 
Chemical composition and norm as on p. 127. 
Type specimen from Fiordine, near Montefiascone, Vulsinian District. 
III. 8. 2. 2. Romal Albanose [Leucltite, Rome Type]. 
Megascopic characters. The rocks which belong to this type are very uniform 
in character megascopically, dense, dark-gray or black basalts, wholly aphyric or 
almost wholly so, the phenocrysts being very rare, small leucites and augites. 
The texture is aphanitic, no distinction between dark and light mineral particles 
being visible to the naked eye or with the hand lens. 
Microscopic characters. In thin section this type presents much the same 
features as those described under galeral braccianose, except that the small amount 
of feldspar visible in that is here totally absent or almost so. The texture is holo- 
crystalline, and the fabric a more or less clathrate one, with the characteristic round 
leucites, though transitions to the xenomorphic granular fabric of the hernical and 
saccal types are not rare. These are somewhat difficult to classify with certainty, 
but the general rule that microphenocrysts of leucite characterize the galeral andromal 
types, and microphenocrysts of augite the hernical and saccal, is a useful diagnostic 
character. The small (0.05 to 0.2 mm.) round leucites are abundant, but relatively 
not as much so as in the corresponding type of braccianose or vesuvose. Skeleton 
development is rather common. Augite microphenocrysts are not abundant, and 
assume the form of stout subhedral or anhedral prismoids, of the usual color and 
optical characters. The greater part of this mineral is in the form of minute prisms 
and grains between the leucites, as already described. Magnetite grains are always 
present, in varying but small amounts, and the same is true of apatite. There is a 
small quantity of colorless, interstitial base, the exact study of which is difficult, 
owing to the felted character of the microgroundmass. In places it appears to be 
plagioclase, again nephelite or glass, though these are rarer, but the amount in any 
case is small. In some specimens there are small patches of yellowish, interstitial 
melilite, marking a transition to the boval type, but in typical ones this is negligible 
or wholly absent. In some instances there may be a trifling amount of interstitial 
brownish biotite. Olivine is sometimes present, in rare small grains, and again 
wholly absent. 
Chemical composition. An analysis of a characteristic specimen of this type 
was made and is given below in I. There is also given for comparison in II an analy- 
sis of the coarse granular type from the Highwood Mountains (missourite), which 
is magmatically very close to the dofemane class, where it was formerly placed,* but 
which the more accurately calculated norm of Pirssonf has shown to be just across 
the border in salfemane, and hence in albanose. To this type the name " missoural 
albanose " may be applied, in recognition of its name in the prevailing systems. 
* Washington, Prof. Paper, U. S. Geol. Surv. No. 14, 1003, p. 355. 
t Pirsson, Bull. U. S. Geol. Surv. No. 237, 1005, p. 120. 
